raven for redux middleware config

raven-middleware.js

import createRavenMiddleware from "raven-for-redux";

export default createRavenMiddleware(window.Raven, {
  stateTransformer: function(state) {
    return Object.assign({}, state, {
      entities: flattenEntities(state.entities)
    });
  },
  actionTransformer: function(action) {
    if (action.response && action.response.entities) {
      return Object.assign({}, action, {
        response: Object.assign({}, action.response, {
          entities: flattenEntities(action.response.entities)
        })
      });
    }
    return action;
  },
  filterBreadcrumbActions: function(action) {
    return !breadcrumbActionBlacklist.includes(action.type);
  }
});

Can you also show your flattenEntities function please?