Oracle Message PLS-00645 - character set mismatch found at string among operands in a COALESCE expression

ERRORcharacter set mismatch found at string among operands in a COALESCE expression
CAUSEIn a COALESCE expression, the operands do not match in character set and it is unclear which implicit conversion is required to correct the mismatch.
ACTIONChange the operands so that their character sets match.