taxonomy_term_save tries to save null parents

The code in taxonomy_term_save does not check to see if the parent variable is not null before it tries to insert data into taxonomy_term_hierarchy. We should check that the parent tid is not null first.

This bug is difficult to reproduce. It occurs SOMETIMES when saving a taxonomy term using the taxonomy_manager module. I chose a taxonomy term on the root level and clicked save. The following error appears. After closing the pop up, the term no longer appears in the taxonomy manager because its taxonomy_term_hierarchy record was deleted.

An AJAX HTTP error occurred.
HTTP Result Code: 500
Debugging information follows.
Path: /system/ajax
StatusText: Service unavailable (with message)
ResponseText: PDOException: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'parent' cannot be null: INSERT INTO {taxonomy_term_hierarchy} (tid, parent) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1); Array
(
[:db_insert_placeholder_0] => 15152
[:db_insert_placeholder_1] =>
)
in taxonomy_term_save() (line 679 of .../modules/taxonomy/taxonomy.module)