Fix analyzer warning on misuse of nullability.

Author: nlutsenko

ParseTwitterUtils/Internal/OAuthCore/PF_OAuthCore.m

@@ -84,7 +84,9 @@ + (NSString *)authorizationHeaderFromConfiguration:(PFOAuthConfiguration *)confi
     // combine all parameters
     NSMutableDictionary *parameters = [oAuthAuthorizationParameters mutableCopy];
     [parameters addEntriesFromDictionary:additionalQueryParameters];
-    [parameters addEntriesFromDictionary:additionalBodyParameters];
+    if (additionalBodyParameters) {
+        [parameters addEntriesFromDictionary:additionalBodyParameters];
+    }
 
     NSArray *sortedKeys = [[parameters allKeys] sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
         return [obj1 compare:obj2] ?: [parameters[obj1] compare:parameters[obj2]];