Change NULL const to NULL_STRING to avoid confusion

ui/src/shared/components/FillQuery.js

@@ -1,7 +1,7 @@
 import React, {Component, PropTypes} from 'react'
 import Dropdown from 'shared/components/Dropdown'
 
-import {NULL, NUMBER} from 'shared/constants/queryFillOptions'
+import {NULL_STRING, NUMBER} from 'shared/constants/queryFillOptions'
 
 import queryFills from 'hson!shared/data/queryFills.hson'
 
@@ -25,7 +25,7 @@ class FillQuery extends Component {
   static defaultProps = {
     size: 'sm',
     theme: 'blue',
-    value: NULL,
+    value: NULL_STRING,
   }
 
   handleDropdown = item => {

ui/src/shared/constants/queryFillOptions.js

@@ -1,5 +1,5 @@
 export const LINEAR = 'linear'
 export const NONE = 'none'
-export const NULL = 'null'
+export const NULL_STRING = 'null'
 export const NUMBER = 'number'
 export const PREVIOUS = 'previous'

ui/src/utils/defaultQueryConfig.js

@@ -1,4 +1,4 @@
-import {NULL} from 'shared/constants/queryFillOptions'
+import {NULL_STRING} from 'shared/constants/queryFillOptions'
 
 const defaultQueryConfig = ({id, isKapacitorRule = false}) => {
   const queryConfig = {
@@ -12,7 +12,7 @@ const defaultQueryConfig = ({id, isKapacitorRule = false}) => {
       time: null,
       tags: [],
     },
-    fill: NULL,
+    fill: NULL_STRING,
     areTagsAccepted: true,
     rawText: null,
     status: null,

ui/src/utils/queryTransitions.js

@@ -1,6 +1,7 @@
 import defaultQueryConfig from 'utils/defaultQueryConfig'
 import {DEFAULT_DASHBOARD_GROUP_BY_INTERVAL} from 'shared/constants'
 import {DEFAULT_DATA_EXPLORER_GROUP_BY_INTERVAL} from 'src/data_explorer/constants'
+import {NULL_STRING} from 'shared/constants/queryFillOptions'
 
 export function editRawText(query, rawText) {
   return Object.assign({}, query, {rawText})