diff --git a/const.go b/const.go
index d4ba9238..6d51f679 100644
--- a/const.go
+++ b/const.go
@@ -147,7 +147,7 @@ const (
 	VERSION_KEY   = "version"
 	TIMEOUT_KEY   = "timeout"
 
-	STRING_NIL   = "null"
+	STRING_NIL   = ""
 	STRING_TRUE  = "true"
 	STRING_FALSE = "false"
 	STRING_ZERO  = "0.0"
diff --git a/java_exception/duplicate_format_flags_exception.go b/java_exception/duplicate_format_flags_exception.go
index 0b774c83..48a6fe0a 100644
--- a/java_exception/duplicate_format_flags_exception.go
+++ b/java_exception/duplicate_format_flags_exception.go
@@ -24,7 +24,7 @@ type DuplicateFormatFlagsException struct {
 }
 
 func (e DuplicateFormatFlagsException) Error() string {
-	if e.DetailMessage == "" || e.DetailMessage == "null" {
+	if e.DetailMessage == "" {
 		return "flags=" + e.Flags
 	} else {
 		return e.DetailMessage + " flags=" + e.Flags
diff --git a/java_exception_test.go b/java_exception_test.go
index 6af78413..6b4e137d 100644
--- a/java_exception_test.go
+++ b/java_exception_test.go
@@ -49,8 +49,8 @@ func TestException(t *testing.T) {
 	doTestException(t, "throw_WriteAbortedException", "writeAbortedException")
 	doTestException(t, "throw_InvalidObjectException", "invalidObjectException")
 	doTestException(t, "throw_StreamCorruptedException", "streamCorruptedException")
-	doTestException(t, "throw_InvalidClassException", "null; invalidClassException")
-	doTestException(t, "throw_OptionalDataException", "null")
+	doTestException(t, "throw_InvalidClassException", "invalidClassException")
+	doTestException(t, "throw_OptionalDataException", "")
 	doTestException(t, "throw_NotActiveException", "notActiveException")
 	doTestException(t, "throw_NotSerializableException", "notSerializableException")
 	doTestException(t, "throw_UTFDataFormatException", "UTFDataFormatException")
@@ -97,7 +97,7 @@ func TestException(t *testing.T) {
 	doTestException(t, "throw_UnsupportedTemporalTypeException", "UnsupportedTemporalTypeException")
 	doTestException(t, "throw_ZoneRulesException", "ZoneRulesException")
 	doTestException(t, "throw_DateTimeParseException", "DateTimeParseException")
-	doTestException(t, "throw_FormatterClosedException", "null")
+	doTestException(t, "throw_FormatterClosedException", "")
 	doTestException(t, "throw_CancellationException", "CancellationException")
 	doTestException(t, "throw_UnknownFormatConversionException", "Conversion = 'UnknownFormatConversionException'")
 	doTestException(t, "throw_UnknownFormatFlagsException", "Flags = UnknownFormatFlagsException")