old_contents: export function nameSpacedTransformer(ns, transformer) {
    if (!transformer) {
      return nameSpacedTransformer.bind(null, ns);
    }
    return (state) => {
      const newState = transformer(state[ns]);
      // nothing has changed
      if (newState === state[ns]) {
        return state;
      }
      return { ...state, [ns]: newState };
    };
  }
  
new_contents: export function nameSpacedTransformer(ns, transformer) {
    if (!transformer) {
      return nameSpacedTransformer.bind(null, ns);
    }
    return (state) => {
      const newState = transformer(state[ns]);
  
      // nothing has changed
      // noop
      if (!newState || newState === state[ns]) {
        return null;
      }
  
      return { ...state, [ns]: newState };
    };
  }
  
subject: Fix for name-spaced transformer