validate method
Returns ErrMap containing the error messages for each field depedning on each its value from ValMap.
Implementation
@override
ErrMap<TKey>? validate(ValMap<TKey> values) {
final masterValue = values.get(master);
final slaveValue = values.get(slave);
if (masterValue != slaveValue) {
return {slave: message};
} else if (masterValue != null && slaveValue != null) {
return {slave: null}; // Clear error
}
return null;
}