Debug info: ERROR: invalid input syntax for integer: ""

SELECT count(userid) FROM mdl_turnitintool_submissions WHERE turnitintoolid=14 AND submission_part=15 AND userid!=0 AND submission_grade IS NOT NULL AND submission_grade>'' 

[array (

)]

Stack trace:

line 394 of /lib/dml/moodle_database.php: dml_read_exception thrown

line 232 of /lib/dml/pgsql_native_moodle_database.php: call to moodle_database->query_end()

line 678 of /lib/dml/pgsql_native_moodle_database.php: call to pgsql_native_moodle_database->query_end()

line 1122 of /lib/dml/moodle_database.php: call to pgsql_native_moodle_database->get_records_sql()

line 6346 of /mod/turnitintool/lib.php: call to moodle_database->get_records_select()

line 795 of /mod/turnitintool/lib.php: call to turnitintool_get_records_select()

line 858 of /course/lib.php: call to turnitintool_print_overview()

line 107 of /blocks/course_overview/block_course_overview.php: call to print_overview()

line 280 of /blocks/moodleblock.class.php: call to block_course_overview->get_content()

line 232 of /blocks/moodleblock.class.php: call to block_base->formatted_contents()

line 924 of /lib/blocklib.php: call to block_base->get_content_for_output()

line 976 of /lib/blocklib.php: call to block_manager->create_block_contents()

line 311 of /lib/blocklib.php: call to block_manager->ensure_content_created()

line 926 of /lib/outputrenderers.php: call to block_manager->get_content_for_region()

line 148 of /my/index.php: call to core_renderer->blocks_for_region()