diff --git a/Pod/Classes/Data/GDCSerializable.h b/Pod/Classes/Data/GDCSerializable.h
index ef21c56..3c09cc8 100644
--- a/Pod/Classes/Data/GDCSerializable.h
+++ b/Pod/Classes/Data/GDCSerializable.h
@@ -4,7 +4,7 @@
 
 #import <Foundation/Foundation.h>
 
-static NSString *const kJsonTypeKey = @"@type";
+static NSString *const _Nonnull kJsonTypeKey = @"@type";
 
 @protocol GDCSerializable <NSObject>
 /// Creates a new instance by parsing Json format. If
@@ -16,7 +16,7 @@ static NSString *const kJsonTypeKey = @"@type";
 ///                 the data can not be parsed.
 ///
 /// @return A new instance of the class messaged.
-+ (instancetype)parseFromJson:(nullable NSDictionary *)json error:(NSError **)errorPtr;
++ (nullable instancetype)parseFromJson:(nullable NSDictionary *)json error:(NSError *_Nullable * _Nullable)errorPtr;
 
 /// Parses json patches of this type and merges it with this message.
 ///
@@ -33,5 +33,5 @@ static NSString *const kJsonTypeKey = @"@type";
 
 /// Merges the fields from another message (of the same type) into this
 /// message.
-- (void)mergeFrom:(id)other;
+- (void)mergeFrom:(nullable id<GDCSerializable>)other;
 @end
\ No newline at end of file
diff --git a/Pod/Classes/Data/GDCUrlCache.h b/Pod/Classes/Data/GDCUrlCache.h
index dd23707..e3e916f 100644
--- a/Pod/Classes/Data/GDCUrlCache.h
+++ b/Pod/Classes/Data/GDCUrlCache.h
@@ -7,7 +7,7 @@
 @class GPBMessage;
 @class GPBFieldMask;
 
-
+NS_ASSUME_NONNULL_BEGIN
 @interface GDCUrlCache : NSObject
 + (GDCUrlCache *)instance;
 
@@ -15,4 +15,5 @@
 
 - (nullable __kindof GPBMessage *)cachedMessageForPath:(NSString *)path andRequest:(GPBMessage *)reqMessage andKeys:(GPBFieldMask *)keys expired:(BOOL *)expired;
 
-@end
\ No newline at end of file
+@end
+NS_ASSUME_NONNULL_END
\ No newline at end of file