Serialized unknown types as strings

When creating a point manually, the field values are interface{}
which allows unsupported types to be passed in.  Previously, the
code would panic.  It will now default to string representation of
the value if it's not a known type.

tsdb/points.go

@@ -1098,7 +1098,11 @@ func (p Fields) MarshalBinary() []byte {
 		case nil:
 			// skip
 		default:
-			panic(fmt.Sprintf("unknown type: %T", v))
+			// Can't determine the type, so convert to string
+			b = append(b, '"')
+			b = append(b, []byte(escapeQuoteString(fmt.Sprintf("%v", v)))...)
+			b = append(b, '"')
+
 		}
 		b = append(b, ',')
 	}

tsdb/points_test.go

@@ -1078,3 +1078,22 @@ func TestNewPointEscaped(t *testing.T) {
 		t.Errorf("NewPoint().String() mismatch.\ngot %v\nexp %v", pt.String(), exp)
 	}
 }
+
+func TestNewPointUnhandledType(t *testing.T) {
+	// nil value
+	pt := NewPoint("cpu", nil, Fields{"value": nil}, time.Unix(0, 0))
+	if exp := `cpu value= 0`; pt.String() != exp {
+		t.Errorf("NewPoint().String() mismatch.\ngot %v\nexp %v", pt.String(), exp)
+	}
+
+	// unsupported type gets stored as string
+	now := time.Unix(0, 0)
+	pt = NewPoint("cpu", nil, Fields{"value": now}, time.Unix(0, 0))
+	if exp := `cpu value="1969-12-31 17:00:00 -0700 MST" 0`; pt.String() != exp {
+		t.Errorf("NewPoint().String() mismatch.\ngot %v\nexp %v", pt.String(), exp)
+	}
+
+	if exp := "1969-12-31 17:00:00 -0700 MST"; pt.Fields()["value"] != exp {
+		t.Errorf("NewPoint().String() mismatch.\ngot %v\nexp %v", pt.String(), exp)
+	}
+}