In bson.c, fromJson calls phongo_throw_exception with either a custom error message, or a generic "Error parsing JSON" message.

To determine whether or not to use a custom error message (bubbled up from mongoc) it checks whether a bson_error_t's message field is NULL. Since the message field is just an array, it is never NULL. This produces a warning on some compilers.

To check if the bson_error_t has an error message, error.code or error.domain should be checked instead.