toString method
A string representation of this object.
Some classes have a default textual representation,
often paired with a static parse function (like int.parse).
These classes will provide the textual representation as
their string representation.
Other classes have no meaningful textual representation
that a program will care about.
Such classes will typically override toString to provide
useful information when inspecting the object,
mainly for debugging or logging.
Implementation
@override
String toString() {
  final $buf = StringBuffer()..writeln('SourceTypeAlipay(');
  if (dataString != null) {
    $buf
      ..writeln()
      ..write('  data_string: ')
      ..write(dataString)
      ..write(',');
  }
  if (nativeUrl != null) {
    $buf
      ..writeln()
      ..write('  native_url: ')
      ..write(nativeUrl)
      ..write(',');
  }
  if (statementDescriptor != null) {
    $buf
      ..writeln()
      ..write('  statement_descriptor: ')
      ..write(statementDescriptor)
      ..write(',');
  }
  $buf.write(')');
  return $buf.toString();
}