get_term_by() returns WP_Error as well

[hakre]

It's not documented, but get_term_by() can return WP_Error as well in case it fails.

Code that checks for the return value only against being not empty is doing short as WP_Error never is empty.

The result are most often undefined property warnings.

The related feature is: Advanced multi-taxonomy WP_Query()s (#12891)

The root cause for this is that get_term() does return WP_Error.

Not that invasive for existing code.

The second patch "corrects" the return value for the function get_term_by() based on the information in the function's docblock comment (return false on error).

Similar: #16282

If that is indeed the only way for get_term_by() to return WP_Error (and that's what it looks like), then the fix looks good. They already needed to look for false anyway, so I'm fine with preventing the possibility of WP_Error being returned through get_term_by().

Duplicate: #16717, Related [17506], [17507]

(updated 1x)

(In [17526]) Return false instead of WP_Error from get_term_by() if the term does not exist. Makes fetching a term by id consistent with slug and name. Props hakre. fixes #16464 #16717 for trunk

(In [17527]) Return false instead of WP_Error from get_term_by() if the term does not exist. Makes fetching a term by id consistent with slug and name. Props hakre. fixes #16464 #16717 for 3.1