title: Cannot read properties of undefined (reading 'map') after adding combineReducers
body: <p>I combined two reducers functions one returning a list of movies and one that I am building to handle the logic enabling users to add a movie to a 'favorites list'.</p>
  <pre><code>import { combineReducers } from 'redux';
  import movieReducer from './movieReducer';
  import movieFavReducer from './movieFavReducer';
  
  //combined reducers 
  export default combineReducers({ movieReducer, movieFavReducer });
  </code></pre>
  <p>If I do not combine these two reducers and just have movieReducer I get all the movies I have, however, the moment I combined these two I get the error message:</p>
  <pre><code>Uncaught TypeError: Cannot read properties of undefined (reading 'map')
  </code></pre>
  <p>This is the relevant code:</p>
  <pre><code>import React from 'react';
  import { connect } from 'react-redux';
  import * as actionCreators from '../actions/movieActions';
  import MovieListItem from './MovieListItem';
  import MovieFooter from './MovieFooter';
  
  const MovieList = (props)=&gt; {
      const{ movies, favorites } = props
      // const movies = [];
  
      return (
          &lt;div className=&quot;col&quot;&gt;
              &lt;table className=&quot;table table-striped table-hover&quot;&gt;
                  &lt;thead&gt;
                  &lt;tr&gt;
                      &lt;th&gt;Title&lt;/th&gt;
                      &lt;th&gt;Director&lt;/th&gt;
                      &lt;th&gt;Genre&lt;/th&gt;
                      &lt;th&gt;Metascore&lt;/th&gt;
                      &lt;th&gt;&lt;/th&gt;
                  &lt;/tr&gt;
                  &lt;/thead&gt;
  
                  &lt;tbody&gt;
                      {
                          props.movies.map(movie=&gt;&lt;MovieListItem key={movie.id} movie={movie}/&gt;)
                      }
                  &lt;/tbody&gt;
              &lt;/table&gt;
              
              &lt;MovieFooter totalMovies={movies.length}/&gt;
          &lt;/div&gt;
      );
  }
  
  //reaching into state and getting specific properties I want
  const mapStateToProps = state =&gt; {
      return {
          movies: state.movies,
          favorites: state.movies
      }
  }
  
  export default connect(mapStateToProps, actionCreators) (MovieList);
  </code></pre>
  <p>I have read solutions suggesting that I first check if movies contains anything before mapping, so something to the tune of <code>movies?.map</code>, the issue is that this nothing, despite the fact that movies are passed down when I don't combine my reducers.</p>
  <p>Please help me figure this out</p>