FILE_TYPE_INVALID_OUTPUT_FILE error condition
The file returned by the UDF cannot be read as a FILE value.
INVALID_PATH
The file '<path>' returned by the UDF is not a valid FILE value.
NOT_FOUND
The file '<path>' was not found or is not a regular file.
REUSED_ACROSS_ROWS
The UDF returned the same FileRef in more than one row. Create a new FileRef for each row.