Message Oracle PLS-00620 - type mismatch found at string among operands in a COALESCE expression

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