docs: private _Private_IonBinaryWriterBuilder fillLegacyDefaults()
      {
          // amzn/ion-java/issues/59 Fix this to use the new writer or eliminate it
  
          // Ensure that we don't modify the user's builder.
          _Private_IonBinaryWriterBuilder b = copy();
  
          if (b.getSymtabValueFactory() == null)
          {
              IonSystem system = IonSystemBuilder.standard().build();
              b.setSymtabValueFactory(system);
          }
  
          SymbolTable initialSymtab = b.getInitialSymbolTable();
          if (initialSymtab == null)
          {
              initialSymtab = initialSymtab(LocalSymbolTable.DEFAULT_LST_FACTORY,
                                            _Private_Utils.systemSymtab(1),
                                            b.getImports());
              b.setInitialSymbolTable(initialSymtab);
          }
          else if (initialSymtab.isSystemTable())
          {
              initialSymtab = initialSymtab(LocalSymbolTable.DEFAULT_LST_FACTORY,
                                            initialSymtab,
                                            b.getImports());
              b.setInitialSymbolTable(initialSymtab);
          }
  
          return b.immutable();
      }