code: private VarSymbol getDefinedSerializableFields(ClassSymbol def) {
          Names names = def.name.table.names;
  
          /* SERIALIZABLE_FIELDS can be private,
           * so must lookup by ClassSymbol, not by ClassDocImpl.
           */
          for (Symbol sym : def.members().getSymbolsByName(names.fromString(SERIALIZABLE_FIELDS))) {
              if (sym.kind == VAR) {
                  VarSymbol f = (VarSymbol)sym;
                  if ((f.flags() & Flags.STATIC) != 0 &&
                      (f.flags() & Flags.PRIVATE) != 0) {
                      return f;
                  }
              }
          }
          return null;
      }
docs: /*
  Check for explicit Serializable fields.
  Check for a private static array of ObjectStreamField with
  name SERIALIZABLE_FIELDS.