I was searching some code snippets with Object search (the logon schema was selected in the left list, only Search source option was selected and job/program/scheduler job and mat.views object types was unselected in the list) which sometimes gives "Could not convert variant of type (Null) into type (OleStr)" error message.
Database|Spool to screen shown the error message with the following query:
Select av.owner, 'VIEW' result_type, 'Source Search' object_type,
av.view_name object_name, av.text text
FROM SYS.DBA_VIEWS av
WHERE av.owner IN ('xx');