Add nonnil markup to ObjC library.
Add the clang annotations to the objc library and generated code to help with Swift bridging and compiler checks.
diff --git a/objectivec/GPBUtilities.h b/objectivec/GPBUtilities.h
index 87cd32c..1301b43 100644
--- a/objectivec/GPBUtilities.h
+++ b/objectivec/GPBUtilities.h
@@ -36,13 +36,16 @@
CF_EXTERN_C_BEGIN
+NS_ASSUME_NONNULL_BEGIN
+
// Generates a string that should be a valid "Text Format" for the C++ version
// of Protocol Buffers. lineIndent can be nil if no additional line indent is
// needed. The comments provide the names according to the ObjC library, they
// most likely won't exactly match the original .proto file.
-NSString *GPBTextFormatForMessage(GPBMessage *message, NSString *lineIndent);
+NSString *GPBTextFormatForMessage(GPBMessage *message,
+ NSString * __nullable lineIndent);
NSString *GPBTextFormatForUnknownFieldSet(GPBUnknownFieldSet *unknownSet,
- NSString *lineIndent);
+ NSString * __nullable lineIndent);
//
// Test if the given field is set on a message.
@@ -128,6 +131,8 @@
// objects.
NSData *GPBEmptyNSData(void) __attribute__((pure));
+NS_ASSUME_NONNULL_END
+
CF_EXTERN_C_END
