Optimize error messages

[clearloop]

@hao-lee that may be true but it is almost irrelevant to this issue. The error message implies the program is not handling the leetcode response correctly and thus it should be fixed.

We could close this issue then the next new user who comes along and hits this error will likely do exactly what the error message tells him, i.e come here and raise another new bug. Is that what we want?

Originally posted by @bulletmark in #57 (comment)