diff --git a/components/802.15.4_RF/atmel-rf-driver/source/NanostackRfPhyAtmel.cpp b/components/802.15.4_RF/atmel-rf-driver/source/NanostackRfPhyAtmel.cpp
index abb2ee93e9..be59a4afcd 100644
--- a/components/802.15.4_RF/atmel-rf-driver/source/NanostackRfPhyAtmel.cpp
+++ b/components/802.15.4_RF/atmel-rf-driver/source/NanostackRfPhyAtmel.cpp
@@ -524,7 +524,7 @@ static void rf_if_reset_radio(void)
 #else
     rf->spi.frequency(MBED_CONF_ATMEL_RF_LOW_SPI_SPEED);
 #endif
-    rf->IRQ.rise(0);
+    rf->IRQ.rise(nullptr);
     rf->RST = 1;
     ThisThread::sleep_for(2);
     rf->RST = 0;
diff --git a/components/wifi/esp8266-driver/ESP8266/ESP8266.cpp b/components/wifi/esp8266-driver/ESP8266/ESP8266.cpp
index 9a31dac111..357db71251 100644
--- a/components/wifi/esp8266-driver/ESP8266/ESP8266.cpp
+++ b/components/wifi/esp8266-driver/ESP8266/ESP8266.cpp
@@ -41,7 +41,7 @@ ESP8266::ESP8266(PinName tx, PinName rx, bool debug, PinName rts, PinName cts)
     : _sdk_v(-1, -1, -1),
       _at_v(-1, -1, -1),
       _tcp_passive(false),
-      _callback(0),
+      _callback(),
       _serial(tx, rx, MBED_CONF_ESP8266_SERIAL_BAUDRATE),
       _serial_rts(rts),
       _serial_cts(cts),
diff --git a/components/wifi/esp8266-driver/ESP8266Interface.cpp b/components/wifi/esp8266-driver/ESP8266Interface.cpp
index 3aeb82a5b9..13ac0bc6b3 100644
--- a/components/wifi/esp8266-driver/ESP8266Interface.cpp
+++ b/components/wifi/esp8266-driver/ESP8266Interface.cpp
@@ -71,7 +71,7 @@ ESP8266Interface::ESP8266Interface()
       _connect_retval(NSAPI_ERROR_OK),
       _disconnect_retval(NSAPI_ERROR_OK),
       _conn_stat(NSAPI_STATUS_DISCONNECTED),
-      _conn_stat_cb(NULL),
+      _conn_stat_cb(),
       _global_event_queue(mbed_event_queue()), // Needs to be set before attaching event() to SIGIO
       _oob_event_id(0),
       _connect_event_id(0),
@@ -113,7 +113,7 @@ ESP8266Interface::ESP8266Interface(PinName tx, PinName rx, bool debug, PinName r
       _connect_retval(NSAPI_ERROR_OK),
       _disconnect_retval(NSAPI_ERROR_OK),
       _conn_stat(NSAPI_STATUS_DISCONNECTED),
-      _conn_stat_cb(NULL),
+      _conn_stat_cb(),
       _global_event_queue(mbed_event_queue()), // Needs to be set before attaching event() to SIGIO
       _oob_event_id(0),
       _connect_event_id(0),
diff --git a/drivers/SerialBase.h b/drivers/SerialBase.h
index e57483ed93..b91304233e 100644
--- a/drivers/SerialBase.h
+++ b/drivers/SerialBase.h
@@ -216,7 +216,7 @@ public:
     /** Begin asynchronous write using 8bit buffer.
      *
      *  The write operation ends with any of the enabled events and invokes
-     *  registered callback function (which can be NULL to not receive callback at all).
+     *  registered callback function (which can be empty to not receive callback at all).
      *  Events that are not enabled by event argument are simply ignored.
      *  Operation has to be ended explicitly by calling abort_write() when
      *  no events are enabled.
@@ -233,7 +233,7 @@ public:
     /** Begin asynchronous write using 16bit buffer.
      *
      *  The write operation ends with any of the enabled events and invokes
-     *  registered callback function (which can be NULL to not receive callback at all).
+     *  registered callback function (which can be empty to not receive callback at all).
      *  Events that are not enabled by event argument are simply ignored.
      *  Operation has to be ended explicitly by calling abort_write() when
      *  no events are enabled.
@@ -256,7 +256,7 @@ public:
     /** Begin asynchronous reading using 8bit buffer.
      *
      *  The read operation ends with any of the enabled events and invokes registered
-     *  callback function (which can be NULL to not receive callback at all).
+     *  callback function (which can be empty to not receive callback at all).
      *  Events that are not enabled by event argument are simply ignored.
      *  Operation has to be ended explicitly by calling abort_read() when
      *  no events are enabled.
@@ -274,7 +274,7 @@ public:
     /** Begin asynchronous reading using 16bit buffer.
      *
      *  The read operation ends with any of the enabled events and invokes registered
-     *  callback function (which can be NULL to not receive callback at all).
+     *  callback function (which can be empty to not receive callback at all).
      *  Events that are not enabled by event argument are simply ignored.
      *  Operation has to be ended explicitly by calling abort_read() when
      *  no events are enabled.
diff --git a/drivers/internal/PolledQueue.h b/drivers/internal/PolledQueue.h
index d8964218b0..97c02a83e0 100644
--- a/drivers/internal/PolledQueue.h
+++ b/drivers/internal/PolledQueue.h
@@ -42,7 +42,7 @@ public:
      *
      *  @param cb Callback called when dispatch needs to be called
      */
-    PolledQueue(mbed::Callback<void()> cb = NULL);
+    PolledQueue(mbed::Callback<void()> cb = nullptr);
 
     virtual ~PolledQueue();
 
diff --git a/drivers/internal/USBDevice.h b/drivers/internal/USBDevice.h
index bc9902e1c8..f03f7f8095 100644
--- a/drivers/internal/USBDevice.h
+++ b/drivers/internal/USBDevice.h
@@ -147,7 +147,7 @@ public:
     * @param callback Method pointer to be called when a packet is transferred
     * @returns true if successful, false otherwise
     */
-    bool endpoint_add(usb_ep_t endpoint, uint32_t max_packet, usb_ep_type_t type, mbed::Callback<void()> callback = NULL);
+    bool endpoint_add(usb_ep_t endpoint, uint32_t max_packet, usb_ep_type_t type, mbed::Callback<void()> callback = nullptr);
 
     /**
     * Add an endpoint
diff --git a/drivers/source/CAN.cpp b/drivers/source/CAN.cpp
index 4dc91810a4..6688829c8e 100644
--- a/drivers/source/CAN.cpp
+++ b/drivers/source/CAN.cpp
@@ -56,7 +56,7 @@ CAN::~CAN()
 
     // Detaching interrupts releases the sleep lock if it was locked
     for (int irq = 0; irq < IrqCnt; irq++) {
-        attach(NULL, (IrqType)irq);
+        attach(nullptr, (IrqType)irq);
     }
     can_irq_free(&_can);
     can_free(&_can);
@@ -147,7 +147,7 @@ void CAN::attach(Callback<void()> func, IrqType type)
         if (_irq[(CanIrqType)type]) {
             sleep_manager_unlock_deep_sleep();
         }
-        _irq[(CanIrqType)type] = NULL;
+        _irq[(CanIrqType)type] = nullptr;
         can_irq_set(&_can, (CanIrqType)type, 0);
     }
     unlock();
diff --git a/drivers/source/InterruptIn.cpp b/drivers/source/InterruptIn.cpp
index a4ab5f0135..113213a289 100644
--- a/drivers/source/InterruptIn.cpp
+++ b/drivers/source/InterruptIn.cpp
@@ -26,8 +26,8 @@ namespace mbed {
 //       constructor, with a default value for the PinMode.
 InterruptIn::InterruptIn(PinName pin) : gpio(),
     gpio_irq(),
-    _rise(NULL),
-    _fall(NULL)
+    _rise(),
+    _fall()
 {
     // No lock needed in the constructor
     irq_init(pin);
@@ -37,8 +37,8 @@ InterruptIn::InterruptIn(PinName pin) : gpio(),
 InterruptIn::InterruptIn(PinName pin, PinMode mode) :
     gpio(),
     gpio_irq(),
-    _rise(NULL),
-    _fall(NULL)
+    _rise(),
+    _fall()
 {
     // No lock needed in the constructor
     irq_init(pin);
@@ -76,7 +76,7 @@ void InterruptIn::rise(Callback<void()> func)
         _rise = func;
         gpio_irq_set(&gpio_irq, IRQ_RISE, 1);
     } else {
-        _rise = NULL;
+        _rise = nullptr;
         gpio_irq_set(&gpio_irq, IRQ_RISE, 0);
     }
     core_util_critical_section_exit();
@@ -89,7 +89,7 @@ void InterruptIn::fall(Callback<void()> func)
         _fall = func;
         gpio_irq_set(&gpio_irq, IRQ_FALL, 1);
     } else {
-        _fall = NULL;
+        _fall = nullptr;
         gpio_irq_set(&gpio_irq, IRQ_FALL, 0);
     }
     core_util_critical_section_exit();
diff --git a/drivers/source/SPI.cpp b/drivers/source/SPI.cpp
index 71f4f76221..cec9518fd0 100644
--- a/drivers/source/SPI.cpp
+++ b/drivers/source/SPI.cpp
@@ -151,14 +151,14 @@ SPI::~SPI()
     lock();
     /* Make sure a stale pointer isn't left in peripheral's owner field */
     if (_peripheral->owner == this) {
-        _peripheral->owner = NULL;
+        _peripheral->owner = nullptr;
     }
     unlock();
 }
 
 SPI::spi_peripheral_s *SPI::_lookup(SPI::SPIName name)
 {
-    SPI::spi_peripheral_s *result = NULL;
+    SPI::spi_peripheral_s *result = nullptr;
     core_util_critical_section_enter();
     for (int idx = 0; idx < _peripherals_used; idx++) {
         if (_peripherals[idx].name == name) {
diff --git a/drivers/source/Serial.cpp b/drivers/source/Serial.cpp
index e972818af1..d76672d060 100644
--- a/drivers/source/Serial.cpp
+++ b/drivers/source/Serial.cpp
@@ -28,11 +28,11 @@ Serial::Serial(const serial_pinmap_t &static_pinmap, const char *name, int baud)
 {
 }
 
-Serial::Serial(PinName tx, PinName rx, int baud): SerialBase(tx, rx, baud), Stream(NULL)
+Serial::Serial(PinName tx, PinName rx, int baud): SerialBase(tx, rx, baud), Stream()
 {
 }
 
-Serial::Serial(const serial_pinmap_t &static_pinmap, int baud): SerialBase(static_pinmap, baud), Stream(NULL)
+Serial::Serial(const serial_pinmap_t &static_pinmap, int baud): SerialBase(static_pinmap, baud), Stream()
 {
 }
 
diff --git a/drivers/source/SerialBase.cpp b/drivers/source/SerialBase.cpp
index 824785139b..dc607224fb 100644
--- a/drivers/source/SerialBase.cpp
+++ b/drivers/source/SerialBase.cpp
@@ -34,21 +34,13 @@ SerialBase::SerialBase(PinName tx, PinName rx, int baud) :
 {
     // No lock needed in the constructor
 
-    for (size_t i = 0; i < sizeof _irq / sizeof _irq[0]; i++) {
-        _irq[i] = NULL;
-    }
-
     (this->*_init_func)();
 }
 
 SerialBase::SerialBase(const serial_pinmap_t &static_pinmap, int baud) :
 #if DEVICE_SERIAL_ASYNCH
-    _thunk_irq(this), _tx_usage(DMA_USAGE_NEVER),
-    _rx_usage(DMA_USAGE_NEVER), _tx_callback(NULL),
-    _rx_callback(NULL), _tx_asynch_set(false),
-    _rx_asynch_set(false),
+    _thunk_irq(this),
 #endif
-    _serial(),
     _baud(baud),
     _tx_pin(static_pinmap.tx_pin),
     _rx_pin(static_pinmap.rx_pin),
@@ -57,10 +49,6 @@ SerialBase::SerialBase(const serial_pinmap_t &static_pinmap, int baud) :
 {
     // No lock needed in the constructor
 
-    for (size_t i = 0; i < sizeof _irq / sizeof _irq[0]; i++) {
-        _irq[i] = NULL;
-    }
-
     (this->*_init_func)();
 }
 
@@ -118,7 +106,7 @@ void SerialBase::attach(Callback<void()> func, IrqType type)
             if (_irq[type]) {
                 sleep_manager_unlock_deep_sleep();
             }
-            _irq[type] = NULL;
+            _irq[type] = nullptr;
             serial_irq_set(&_serial, (SerialIrq)type, 0);
         }
         core_util_critical_section_exit();
@@ -187,7 +175,7 @@ void SerialBase::enable_input(bool enable)
         core_util_critical_section_enter();
         if (enable) {
             // Enable rx IRQ and lock deep sleep if a rx handler is attached
-            // (indicated by rx IRQ callback not NULL)
+            // (indicated by rx IRQ callback not empty)
             if (_irq[RxIrq]) {
                 _irq[RxIrq].call();
                 sleep_manager_lock_deep_sleep();
@@ -197,7 +185,7 @@ void SerialBase::enable_input(bool enable)
             // Disable rx IRQ
             serial_irq_set(&_serial, (SerialIrq)RxIrq, 0);
             // Unlock deep sleep if a rx handler is attached
-            // (indicated by rx IRQ callback not NULL)
+            // (indicated by rx IRQ callback not empty)
             if (_irq[RxIrq]) {
                 sleep_manager_unlock_deep_sleep();
             }
@@ -224,7 +212,7 @@ void SerialBase::enable_output(bool enable)
         core_util_critical_section_enter();
         if (enable) {
             // Enable tx IRQ and lock deep sleep if a tx handler is attached
-            // (indicated by tx IRQ callback not NULL)
+            // (indicated by tx IRQ callback not empty)
             if (_irq[TxIrq]) {
                 _irq[TxIrq].call();
                 sleep_manager_lock_deep_sleep();
@@ -234,7 +222,7 @@ void SerialBase::enable_output(bool enable)
             // Disable tx IRQ
             serial_irq_set(&_serial, (SerialIrq)TxIrq, 0);
             // Unlock deep sleep if a tx handler is attached
-            // (indicated by tx IRQ callback not NULL)
+            // (indicated by tx IRQ callback not empty)
             if (_irq[TxIrq]) {
                 sleep_manager_unlock_deep_sleep();
             }
@@ -297,7 +285,7 @@ SerialBase::~SerialBase()
 
     // Detaching interrupts releases the sleep lock if it was locked
     for (int irq = 0; irq < IrqCnt; irq++) {
-        attach(NULL, (IrqType)irq);
+        attach(nullptr, (IrqType)irq);
     }
 }
 
@@ -389,7 +377,7 @@ void SerialBase::abort_write(void)
     lock();
     core_util_critical_section_enter();
     if (_tx_asynch_set) {
-        _tx_callback = NULL;
+        _tx_callback = nullptr;
         _tx_asynch_set = false;
         serial_tx_abort_asynch(&_serial);
         sleep_manager_unlock_deep_sleep();
@@ -403,7 +391,7 @@ void SerialBase::abort_read(void)
     lock();
     core_util_critical_section_enter();
     if (_rx_asynch_set) {
-        _rx_callback = NULL;
+        _rx_callback = nullptr;
         _rx_asynch_set = false;
         serial_rx_abort_asynch(&_serial);
         sleep_manager_unlock_deep_sleep();
@@ -475,7 +463,7 @@ void SerialBase::interrupt_handler_asynch(void)
     if (_rx_asynch_set && rx_event) {
         event_callback_t cb = _rx_callback;
         _rx_asynch_set = false;
-        _rx_callback = NULL;
+        _rx_callback = nullptr;
         if (cb) {
             cb.call(rx_event);
         }
@@ -486,7 +474,7 @@ void SerialBase::interrupt_handler_asynch(void)
     if (_tx_asynch_set && tx_event) {
         event_callback_t cb = _tx_callback;
         _tx_asynch_set = false;
-        _tx_callback = NULL;
+        _tx_callback = nullptr;
         if (cb) {
             cb.call(tx_event);
         }
diff --git a/drivers/source/Ticker.cpp b/drivers/source/Ticker.cpp
index 3114abdf33..47b4960295 100644
--- a/drivers/source/Ticker.cpp
+++ b/drivers/source/Ticker.cpp
@@ -23,12 +23,12 @@
 
 namespace mbed {
 
-Ticker::Ticker() : TimerEvent(), _delay(0), _function(0), _lock_deepsleep(true)
+Ticker::Ticker() : TimerEvent(), _delay(0), _lock_deepsleep(true)
 {
 }
 
 // When low power ticker is in use, then do not disable deep sleep.
-Ticker::Ticker(const ticker_data_t *data) : TimerEvent(data), _delay(0), _function(0), _lock_deepsleep(!data->interface->runs_in_deep_sleep)
+Ticker::Ticker(const ticker_data_t *data) : TimerEvent(data), _delay(0), _lock_deepsleep(!data->interface->runs_in_deep_sleep)
 {
 }
 
diff --git a/drivers/source/UARTSerial.cpp b/drivers/source/UARTSerial.cpp
index 91be64e083..e9036e3ece 100644
--- a/drivers/source/UARTSerial.cpp
+++ b/drivers/source/UARTSerial.cpp
@@ -67,7 +67,7 @@ void UARTSerial::set_baud(int baud)
 void UARTSerial::set_data_carrier_detect(PinName dcd_pin, bool active_high)
 {
     delete _dcd_irq;
-    _dcd_irq = NULL;
+    _dcd_irq = nullptr;
 
     if (dcd_pin != NC) {
         _dcd_irq = new InterruptIn(dcd_pin);
@@ -361,7 +361,7 @@ void UARTSerial::enable_rx_irq()
 
 void UARTSerial::disable_rx_irq()
 {
-    SerialBase::attach(NULL, RxIrq);
+    SerialBase::attach(nullptr, RxIrq);
     _rx_irq_enabled = false;
 }
 
@@ -373,7 +373,7 @@ void UARTSerial::enable_tx_irq()
 
 void UARTSerial::disable_tx_irq()
 {
-    SerialBase::attach(NULL, TxIrq);
+    SerialBase::attach(nullptr, TxIrq);
     _tx_irq_enabled = false;
 }
 
diff --git a/drivers/source/usb/AsyncOp.cpp b/drivers/source/usb/AsyncOp.cpp
index 229d5c7062..351dff32f7 100644
--- a/drivers/source/usb/AsyncOp.cpp
+++ b/drivers/source/usb/AsyncOp.cpp
@@ -85,9 +85,9 @@ void AsyncOp::complete()
     core_util_critical_section_enter();
 
     mbed::Callback<void()> cb = _callback;
-    _callback = NULL;
-    _list = NULL;
-    if (_wait != NULL) {
+    _callback = nullptr;
+    _list = nullptr;
+    if (_wait != nullptr) {
         _wait->release();
     }
 
@@ -115,11 +115,11 @@ void AsyncOp::_abort(bool timeout)
     core_util_critical_section_enter();
     OperationListBase *list = _list;
     if (list) {
-        _callback = NULL;
+        _callback = nullptr;
         _aborted = true;
-        _wait = NULL;
+        _wait = nullptr;
         _timeout = timeout;
-        _list = NULL;
+        _list = nullptr;
     }
     core_util_critical_section_exit();
     if (list) {
diff --git a/drivers/source/usb/USBDevice.cpp b/drivers/source/usb/USBDevice.cpp
index 40c3b0df93..6d3cfc87d4 100644
--- a/drivers/source/usb/USBDevice.cpp
+++ b/drivers/source/usb/USBDevice.cpp
@@ -1177,7 +1177,7 @@ void USBDevice::endpoint_remove(usb_ep_t endpoint)
         _phy->endpoint_abort(endpoint);
     }
 
-    info->callback = NULL;
+    info->callback = nullptr;
     info->flags = 0;
     info->pending = 0;
     info->max_packet_size = 0;
diff --git a/features/cellular/framework/AT/AT_CellularDevice.cpp b/features/cellular/framework/AT/AT_CellularDevice.cpp
index 2aed8c7042..b4b5375c6d 100644
--- a/features/cellular/framework/AT/AT_CellularDevice.cpp
+++ b/features/cellular/framework/AT/AT_CellularDevice.cpp
@@ -53,10 +53,10 @@ AT_CellularDevice::AT_CellularDevice(FileHandle *fh) : CellularDevice(fh),
 AT_CellularDevice::~AT_CellularDevice()
 {
     if (get_property(PROPERTY_AT_CGEREP)) {
-        _at->set_urc_handler("+CGEV: NW DEACT", 0);
-        _at->set_urc_handler("+CGEV: ME DEACT", 0);
-        _at->set_urc_handler("+CGEV: NW PDN D", 0);
-        _at->set_urc_handler("+CGEV: ME PDN D", 0);
+        _at->set_urc_handler("+CGEV: NW DEACT", nullptr);
+        _at->set_urc_handler("+CGEV: ME DEACT", nullptr);
+        _at->set_urc_handler("+CGEV: NW PDN D", nullptr);
+        _at->set_urc_handler("+CGEV: ME PDN D", nullptr);
     }
 
     // make sure that all is deleted even if somewhere close was not called and reference counting is messed up.
diff --git a/features/cellular/framework/AT/AT_CellularNetwork.cpp b/features/cellular/framework/AT/AT_CellularNetwork.cpp
index d91b45d093..a2b6f3577f 100644
--- a/features/cellular/framework/AT/AT_CellularNetwork.cpp
+++ b/features/cellular/framework/AT/AT_CellularNetwork.cpp
@@ -72,7 +72,7 @@ static const char *const rat_str[AT_CellularNetwork::RAT_MAX] = {
 
 
 AT_CellularNetwork::AT_CellularNetwork(ATHandler &atHandler, AT_CellularDevice &device) :
-    _connection_status_cb(NULL), _ciotopt_network_support_cb(NULL), _op_act(RAT_UNKNOWN),
+    _connection_status_cb(), _ciotopt_network_support_cb(), _op_act(RAT_UNKNOWN),
     _connect_status(NSAPI_STATUS_DISCONNECTED), _supported_network_opt(CIOT_OPT_MAX),
     _at(atHandler), _device(device)
 {
@@ -101,15 +101,15 @@ AT_CellularNetwork::~AT_CellularNetwork()
     (void)set_packet_domain_event_reporting(false);
     for (int type = 0; type < CellularNetwork::C_MAX; type++) {
         if (_device.get_property((AT_CellularDevice::CellularProperty)type) != RegistrationModeDisable) {
-            _at.set_urc_handler(at_reg[type].urc_prefix, 0);
+            _at.set_urc_handler(at_reg[type].urc_prefix, nullptr);
         }
     }
 
     if (_device.get_property(AT_CellularDevice::PROPERTY_AT_CGEREP)) {
-        _at.set_urc_handler("+CGEV: ME DET", 0);
-        _at.set_urc_handler("+CGEV: NW DET", 0);
+        _at.set_urc_handler("+CGEV: ME DET", nullptr);
+        _at.set_urc_handler("+CGEV: NW DET", nullptr);
     }
-    _at.set_urc_handler("+CCIOTOPTI:", 0);
+    _at.set_urc_handler("+CCIOTOPTI:", nullptr);
 }
 
 void AT_CellularNetwork::urc_cgev()
diff --git a/features/cellular/framework/AT/AT_CellularSMS.cpp b/features/cellular/framework/AT/AT_CellularSMS.cpp
index af526013ab..142d920b94 100644
--- a/features/cellular/framework/AT/AT_CellularSMS.cpp
+++ b/features/cellular/framework/AT/AT_CellularSMS.cpp
@@ -177,7 +177,7 @@ static const unsigned char gsm_to_ascii[] = {
 
 const int GSM_TO_ASCII_TABLE_SIZE = sizeof(gsm_to_ascii) / sizeof(gsm_to_ascii[0]);
 
-AT_CellularSMS::AT_CellularSMS(ATHandler &at, AT_CellularDevice &device) : _cb(0), _mode(CellularSMSMmodeText),
+AT_CellularSMS::AT_CellularSMS(ATHandler &at, AT_CellularDevice &device) : _cb(), _mode(CellularSMSMmodeText),
     _use_8bit_encoding(false), _sim_wait_time(0), _sms_message_ref_number(1),
     _sms_info(NULL), _at(at), _device(device)
 {
diff --git a/features/cellular/framework/device/ATHandler.cpp b/features/cellular/framework/device/ATHandler.cpp
index c24eb9152a..1fe82c2c2d 100644
--- a/features/cellular/framework/device/ATHandler.cpp
+++ b/features/cellular/framework/device/ATHandler.cpp
@@ -291,7 +291,7 @@ void ATHandler::set_is_filehandle_usable(bool usable)
             _fileHandle->sigio(Callback<void()>(this, &ATHandler::event));
         } else {
             _fileHandle->set_blocking(true); // set back to default state
-            _fileHandle->sigio(NULL);
+            _fileHandle->sigio(nullptr);
         }
         _is_fh_usable = usable;
     }
diff --git a/features/cellular/framework/device/CellularContext.cpp b/features/cellular/framework/device/CellularContext.cpp
index 35c174b0b1..f5a65c0f44 100644
--- a/features/cellular/framework/device/CellularContext.cpp
+++ b/features/cellular/framework/device/CellularContext.cpp
@@ -59,12 +59,11 @@ MBED_WEAK CellularContext *CellularContext::get_default_nonip_instance()
 }
 
 CellularContext::CellularContext() : _next(0), _stack(0), _pdp_type(DEFAULT_PDP_TYPE),
-    _authentication_type(CellularContext::CHAP), _connect_status(NSAPI_STATUS_DISCONNECTED), _status_cb(0),
+    _authentication_type(CellularContext::CHAP), _connect_status(NSAPI_STATUS_DISCONNECTED), _status_cb(),
     _cid(-1), _new_context_set(false), _is_context_active(false), _is_context_activated(false),
-    _apn(0), _uname(0), _pwd(0), _dcd_pin(NC), _active_high(false), _cp_netif(0), _retry_array_length(0),
-    _retry_count(0), _device(0), _nw(0), _is_blocking(true), _nonip_req(false), _cp_in_use(false)
+    _apn(0), _uname(0), _pwd(0), _dcd_pin(NC), _active_high(false), _cp_netif(0), _retry_timeout_array(),
+    _retry_array_length(0), _retry_count(0), _device(0), _nw(0), _is_blocking(true), _nonip_req(false), _cp_in_use(false)
 {
-    memset(_retry_timeout_array, 0, sizeof(_retry_timeout_array));
 }
 
 void CellularContext::cp_data_received()
diff --git a/features/cellular/framework/device/CellularDevice.cpp b/features/cellular/framework/device/CellularDevice.cpp
index 602a3e38a1..4ceaaca081 100644
--- a/features/cellular/framework/device/CellularDevice.cpp
+++ b/features/cellular/framework/device/CellularDevice.cpp
@@ -40,7 +40,7 @@ CellularDevice::CellularDevice(FileHandle *fh) :
     _sms_ref_count(0),
 #endif //MBED_CONF_CELLULAR_USE_SMS
     _info_ref_count(0), _fh(fh), _queue(10 * EVENTS_EVENT_SIZE), _state_machine(0),
-    _status_cb(0), _nw(0)
+    _status_cb(), _nw(0)
 #ifdef MBED_CONF_RTOS_PRESENT
     , _queue_thread(osPriorityNormal, 2048, NULL, "cellular_queue")
 #endif // MBED_CONF_RTOS_PRESENT
diff --git a/features/cellular/framework/device/CellularStateMachine.cpp b/features/cellular/framework/device/CellularStateMachine.cpp
index dd8696e8cd..dded03921b 100644
--- a/features/cellular/framework/device/CellularStateMachine.cpp
+++ b/features/cellular/framework/device/CellularStateMachine.cpp
@@ -50,7 +50,7 @@ namespace mbed {
 
 CellularStateMachine::CellularStateMachine(CellularDevice &device, events::EventQueue &queue, CellularNetwork &nw) :
     _cellularDevice(device), _state(STATE_INIT), _next_state(_state), _target_state(_state),
-    _event_status_cb(0), _network(nw), _queue(queue), _sim_pin(0), _retry_count(0),
+    _event_status_cb(), _network(nw), _queue(queue), _sim_pin(0), _retry_count(0),
     _event_timeout(-1), _event_id(-1), _plmn(0), _command_success(false),
     _is_retry(false), _cb_data(), _current_event(CellularDeviceReady), _status(0)
 {
@@ -345,7 +345,7 @@ bool CellularStateMachine::device_ready()
 #endif // MBED_CONF_CELLULAR_DEBUG_AT
 
     send_event_cb(CellularDeviceReady);
-    _cellularDevice.set_ready_cb(0);
+    _cellularDevice.set_ready_cb(nullptr);
 
     return true;
 }
diff --git a/features/cellular/framework/targets/GEMALTO/CINTERION/GEMALTO_CINTERION_CellularStack.cpp b/features/cellular/framework/targets/GEMALTO/CINTERION/GEMALTO_CINTERION_CellularStack.cpp
index 54674199d4..c0e10d71ed 100644
--- a/features/cellular/framework/targets/GEMALTO/CINTERION/GEMALTO_CINTERION_CellularStack.cpp
+++ b/features/cellular/framework/targets/GEMALTO/CINTERION/GEMALTO_CINTERION_CellularStack.cpp
@@ -35,9 +35,9 @@ GEMALTO_CINTERION_CellularStack::GEMALTO_CINTERION_CellularStack(ATHandler &atHa
 
 GEMALTO_CINTERION_CellularStack::~GEMALTO_CINTERION_CellularStack()
 {
-    _at.set_urc_handler("^SIS:", 0);
-    _at.set_urc_handler("^SISW:", 0);
-    _at.set_urc_handler("^SISR:", 0);
+    _at.set_urc_handler("^SIS:", nullptr);
+    _at.set_urc_handler("^SISW:", nullptr);
+    _at.set_urc_handler("^SISR:", nullptr);
 }
 
 void GEMALTO_CINTERION_CellularStack::urc_sis()
diff --git a/features/cellular/framework/targets/QUECTEL/BC95/QUECTEL_BC95_CellularStack.cpp b/features/cellular/framework/targets/QUECTEL/BC95/QUECTEL_BC95_CellularStack.cpp
index 2f4e3550a4..7c25bc627a 100644
--- a/features/cellular/framework/targets/QUECTEL/BC95/QUECTEL_BC95_CellularStack.cpp
+++ b/features/cellular/framework/targets/QUECTEL/BC95/QUECTEL_BC95_CellularStack.cpp
@@ -48,8 +48,8 @@ QUECTEL_BC95_CellularStack::~QUECTEL_BC95_CellularStack()
         _event_queue->cancel(_txfull_event_id);
     }
 
-    _at.set_urc_handler("+NSONMI:", NULL);
-    _at.set_urc_handler("+NSOCLI:", NULL);
+    _at.set_urc_handler("+NSONMI:", nullptr);
+    _at.set_urc_handler("+NSOCLI:", nullptr);
 }
 
 nsapi_error_t QUECTEL_BC95_CellularStack::socket_listen(nsapi_socket_t handle, int backlog)
diff --git a/features/cellular/framework/targets/QUECTEL/BG96/QUECTEL_BG96_CellularContext.cpp b/features/cellular/framework/targets/QUECTEL/BG96/QUECTEL_BG96_CellularContext.cpp
index f7ed3b40c7..72ba2458a5 100644
--- a/features/cellular/framework/targets/QUECTEL/BG96/QUECTEL_BG96_CellularContext.cpp
+++ b/features/cellular/framework/targets/QUECTEL/BG96/QUECTEL_BG96_CellularContext.cpp
@@ -39,7 +39,7 @@ QUECTEL_BG96_CellularContext::QUECTEL_BG96_CellularContext(ATHandler &at, Cellul
 QUECTEL_BG96_CellularContext::~QUECTEL_BG96_CellularContext()
 {
     if (_nonip_req) {
-        _at.set_urc_handler("+QIND:", 0);
+        _at.set_urc_handler("+QIND:", nullptr);
     }
 }
 
diff --git a/features/cellular/framework/targets/QUECTEL/M26/QUECTEL_M26_CellularStack.cpp b/features/cellular/framework/targets/QUECTEL/M26/QUECTEL_M26_CellularStack.cpp
index 83ed44a19c..45bee63716 100644
--- a/features/cellular/framework/targets/QUECTEL/M26/QUECTEL_M26_CellularStack.cpp
+++ b/features/cellular/framework/targets/QUECTEL/M26/QUECTEL_M26_CellularStack.cpp
@@ -39,14 +39,14 @@ QUECTEL_M26_CellularStack::QUECTEL_M26_CellularStack(ATHandler &atHandler, int c
 
 QUECTEL_M26_CellularStack::~QUECTEL_M26_CellularStack()
 {
-    _at.set_urc_handler("5, CLOSED", NULL);
-    _at.set_urc_handler("4, CLOSED", NULL);
-    _at.set_urc_handler("3, CLOSED", NULL);
-    _at.set_urc_handler("2, CLOSED", NULL);
-    _at.set_urc_handler("1, CLOSED", NULL);
-    _at.set_urc_handler("0, CLOSED", NULL);
+    _at.set_urc_handler("5, CLOSED", nullptr);
+    _at.set_urc_handler("4, CLOSED", nullptr);
+    _at.set_urc_handler("3, CLOSED", nullptr);
+    _at.set_urc_handler("2, CLOSED", nullptr);
+    _at.set_urc_handler("1, CLOSED", nullptr);
+    _at.set_urc_handler("0, CLOSED", nullptr);
 
-    _at.set_urc_handler("+QIRDI:", NULL);
+    _at.set_urc_handler("+QIRDI:", nullptr);
 }
 
 nsapi_error_t QUECTEL_M26_CellularStack::socket_listen(nsapi_socket_t handle, int backlog)
diff --git a/features/cellular/framework/targets/UBLOX/N2XX/UBLOX_N2XX.cpp b/features/cellular/framework/targets/UBLOX/N2XX/UBLOX_N2XX.cpp
index c27182c093..b100ca9958 100644
--- a/features/cellular/framework/targets/UBLOX/N2XX/UBLOX_N2XX.cpp
+++ b/features/cellular/framework/targets/UBLOX/N2XX/UBLOX_N2XX.cpp
@@ -52,7 +52,7 @@ void UBLOX_N2XX::set_at_urcs_impl()
 
 UBLOX_N2XX::~UBLOX_N2XX()
 {
-    _at->set_urc_handler("+NPIN:", NULL);
+    _at->set_urc_handler("+NPIN:", nullptr);
 }
 
 // Callback for Sim Pin.
diff --git a/features/cellular/framework/targets/UBLOX/N2XX/UBLOX_N2XX_CellularStack.cpp b/features/cellular/framework/targets/UBLOX/N2XX/UBLOX_N2XX_CellularStack.cpp
index de9d65ec6f..c3fc9df5ce 100644
--- a/features/cellular/framework/targets/UBLOX/N2XX/UBLOX_N2XX_CellularStack.cpp
+++ b/features/cellular/framework/targets/UBLOX/N2XX/UBLOX_N2XX_CellularStack.cpp
@@ -31,7 +31,7 @@ UBLOX_N2XX_CellularStack::UBLOX_N2XX_CellularStack(ATHandler &atHandler, int cid
 
 UBLOX_N2XX_CellularStack::~UBLOX_N2XX_CellularStack()
 {
-    _at.set_urc_handler("+NSONMI:", NULL);
+    _at.set_urc_handler("+NSONMI:", nullptr);
 }
 
 nsapi_error_t UBLOX_N2XX_CellularStack::socket_listen(nsapi_socket_t handle, int backlog)
diff --git a/features/netsocket/nsapi_ppp.h b/features/netsocket/nsapi_ppp.h
index 8d47dffe6a..b23a03ac86 100644
--- a/features/netsocket/nsapi_ppp.h
+++ b/features/netsocket/nsapi_ppp.h
@@ -47,7 +47,7 @@ nsapi_error_t nsapi_ppp_set_blocking(bool blocking);
  *
  *  @return             0 on success, negative error code on failure
  */
-nsapi_error_t nsapi_ppp_connect(FileHandle *stream, Callback<void(nsapi_event_t, intptr_t)> status_cb = 0, const char *uname = 0, const char *pwd = 0, const nsapi_ip_stack_t stack = DEFAULT_STACK);
+nsapi_error_t nsapi_ppp_connect(FileHandle *stream, Callback<void(nsapi_event_t, intptr_t)> status_cb = nullptr, const char *uname = 0, const char *pwd = 0, const nsapi_ip_stack_t stack = DEFAULT_STACK);
 
 /** Close a PPP connection
  *
diff --git a/features/storage/filesystem/fat/FATFileSystem.cpp b/features/storage/filesystem/fat/FATFileSystem.cpp
index 1a77738e08..88dbdebcbd 100644
--- a/features/storage/filesystem/fat/FATFileSystem.cpp
+++ b/features/storage/filesystem/fat/FATFileSystem.cpp
@@ -93,7 +93,7 @@ public:
     Deferred &operator=(const Deferred &);
 
 public:
-    Deferred(T t, Callback<void(T)> ondefer = NULL)
+    Deferred(T t, Callback<void(T)> ondefer = nullptr)
         : _t(t), _ondefer(ondefer)
     {
     }
diff --git a/platform/SharedPtr.h b/platform/SharedPtr.h
index 22f81f9ec3..73a3b3c80d 100644
--- a/platform/SharedPtr.h
+++ b/platform/SharedPtr.h
@@ -44,9 +44,9 @@ namespace mbed {
   *     // Increase reference count
   *     SharedPtr<MyStruct> ptr2( ptr );
   *
-  *     ptr = NULL; // Reference to the struct instance is still held by ptr2
+  *     ptr = nullptr; // Reference to the struct instance is still held by ptr2
   *
-  *     ptr2 = NULL; // The raw pointer is freed
+  *     ptr2 = nullptr; // The raw pointer is freed
   * }
   * @endcode
   *