message: java core: Add doc for simple/omitted/=nothing interaction
diff: @@ -49,6 +49,13 @@ public final class SimpleBinaryWriter implements ProtocolWriter {
  @Override
  public void writeFieldOmitted(
  final BondDataType type, final int id, final FieldMetadata metadata) throws IOException {
  + // Simple doesn't support omitting fields, so we need to explicitly write the default values
  + // for optional fields.
  + //
  + // Fields that are = nothing have no default, so it is an unrecoverable error to attempt to
  + // serialize such a field if it is actually set to nothing (e.g., a SomethingObject which is
  + // null).
  +
  if (metadata.isDefaultNothing()) {
  throw new IllegalArgumentException("can't omit fields with default = nothing in SimpleBinary");
  }
  