This check compares the return type specified in the @return annotation of a function
or method doc comment with the types returned by the function and raises an issue if they
mismatch.
The return type could not be reliably inferred; please add a @return annotation.
Our type inference engine in quite powerful, but sometimes the code does not
provide enough clues to go by. In these cases we request you to add a @return
annotation as described here.