support null timestamp types

conn.go

@@ -361,10 +361,14 @@ var doubleConverter = valueConverterFunc(func(val interface{}) (driver.Value, er
 
 // timestampConverter converts a value from the underlying json response into a time.Time.
 var timestampConverter = valueConverterFunc(func(val interface{}) (driver.Value, error) {
+	if val == nil {
+		return nil, nil
+	}
 	if vv, ok := val.(string); ok {
 		// BUG: should parse using session time zone.
-		ts, err := time.ParseInLocation("2006-01-02 15:04:05.000", vv, time.Local)
-		return ts, err
+		if ts, err := time.ParseInLocation("2006-01-02 15:04:05.000", vv, time.Local); err == nil {
+			return ts, nil
+		}
 	}
 	return nil, fmt.Errorf("%s: failed to convert %v (%T) into type time.Time", DriverName, val, val)
 })

conn_test.go

@@ -491,3 +491,61 @@ func TestBigIntConverter(t *testing.T) {
 
 	}
 }
+
+func TestTimestampConverter(t *testing.T) {
+	testCases := []struct {
+		val      interface{}
+		expected driver.Value
+		err      bool
+	}{
+
+		{
+			val:      "2015-04-23 10:00:08.123",
+			expected: time.Date(2015, 04, 23, 10, 0, 8, int(123*time.Millisecond), time.Local),
+			err:      false,
+		},
+
+		{
+			val:      1000.0,
+			expected: nil,
+			err:      true,
+		},
+
+		{
+			val:      "foo",
+			expected: nil,
+			err:      true,
+		},
+
+		{
+			val:      "Infinity",
+			expected: nil,
+			err:      true,
+		},
+
+		{
+			val:      "NaN",
+			expected: nil,
+			err:      true,
+		},
+
+		{
+			val:      nil,
+			expected: nil,
+			err:      false,
+		},
+	}
+
+	for _, tc := range testCases {
+		v, err := timestampConverter(tc.val)
+
+		if tc.err == (err == nil) {
+			t.Errorf("%v: got error %v, wanted %v", tc.val, err, tc.err)
+		}
+
+		if v != tc.expected {
+			t.Errorf("%v: got %v, wanted %v", tc.val, v, tc.expected)
+		}
+
+	}
+}