Oracle Message PLS-00630 - pipelined functions must have a supported collection return type

ERRORpipelined functions must have a supported collection return type
CAUSEA pipelined function was specified with an unsupported return type. The following are not supported as return types of pipelined functions: - non-collections, - PL/SQL tables, - associative arrays, - collections of PL/SQL types: rowid, mlslabel, long, long raw, boolean, binary_integer, pls_integer, string and urowid The following restrictions apply: - If the return type is a collection of records, then each of the attributes of the record must be a supported type. - A collection of records must not contain a record type as one of its attributes.
ACTIONSpecify a supported collection type as the pipelined function return type.