Fix to use "nil" instead of "NULL" for objc objects.
diff --git a/objectivec/google/protobuf/Struct.pbobjc.m b/objectivec/google/protobuf/Struct.pbobjc.m
index 6d9d7b7..816fd6d 100644
--- a/objectivec/google/protobuf/Struct.pbobjc.m
+++ b/objectivec/google/protobuf/Struct.pbobjc.m
@@ -53,7 +53,7 @@
 #pragma mark - Enum GPBNullValue
 
 GPBEnumDescriptor *GPBNullValue_EnumDescriptor(void) {
-  static _Atomic(GPBEnumDescriptor*) descriptor = NULL;
+  static _Atomic(GPBEnumDescriptor*) descriptor = nil;
   if (!descriptor) {
     static const char *valueNames =
         "NullValue\000";
diff --git a/objectivec/google/protobuf/Type.pbobjc.m b/objectivec/google/protobuf/Type.pbobjc.m
index 981ae4d..bb64d87 100644
--- a/objectivec/google/protobuf/Type.pbobjc.m
+++ b/objectivec/google/protobuf/Type.pbobjc.m
@@ -56,7 +56,7 @@
 #pragma mark - Enum GPBSyntax
 
 GPBEnumDescriptor *GPBSyntax_EnumDescriptor(void) {
-  static _Atomic(GPBEnumDescriptor*) descriptor = NULL;
+  static _Atomic(GPBEnumDescriptor*) descriptor = nil;
   if (!descriptor) {
     static const char *valueNames =
         "SyntaxProto2\000SyntaxProto3\000";
@@ -371,7 +371,7 @@
 #pragma mark - Enum GPBField_Kind
 
 GPBEnumDescriptor *GPBField_Kind_EnumDescriptor(void) {
-  static _Atomic(GPBEnumDescriptor*) descriptor = NULL;
+  static _Atomic(GPBEnumDescriptor*) descriptor = nil;
   if (!descriptor) {
     static const char *valueNames =
         "TypeUnknown\000TypeDouble\000TypeFloat\000TypeInt"
@@ -445,7 +445,7 @@
 #pragma mark - Enum GPBField_Cardinality
 
 GPBEnumDescriptor *GPBField_Cardinality_EnumDescriptor(void) {
-  static _Atomic(GPBEnumDescriptor*) descriptor = NULL;
+  static _Atomic(GPBEnumDescriptor*) descriptor = nil;
   if (!descriptor) {
     static const char *valueNames =
         "CardinalityUnknown\000CardinalityOptional\000C"
diff --git a/src/google/protobuf/compiler/objectivec/objectivec_enum.cc b/src/google/protobuf/compiler/objectivec/objectivec_enum.cc
index 95e53f1..978e985 100644
--- a/src/google/protobuf/compiler/objectivec/objectivec_enum.cc
+++ b/src/google/protobuf/compiler/objectivec/objectivec_enum.cc
@@ -149,7 +149,7 @@
 
   printer->Print(
       "GPBEnumDescriptor *$name$_EnumDescriptor(void) {\n"
-      "  static _Atomic(GPBEnumDescriptor*) descriptor = NULL;\n"
+      "  static _Atomic(GPBEnumDescriptor*) descriptor = nil;\n"
       "  if (!descriptor) {\n",
       "name", name_);