Oracle Message PLS-00616 - type mismatch found at string among result expressions in a CASE expression

ERRORtype mismatch found at string among result expressions in a CASE expression
CAUSEIn a CASE expression, the result expressions do not match in datatype, and it is unclear which implicit conversion is required to correct the mismatch.
ACTIONChange the result expressions so that their datatypes match. Consider using datatype conversion functions in the result expressions.