title: Wordpress wp_query() multiple post-types with specific taxonomy terms
body: <p>I'm trying to create a Wordpress query that includes all the standard blog posts and also the custom-post-type 'podcast' which have the taxonomy of 'series' and term 'video-blogs'. So far I've got:</p>
  
  <pre><code>$custom_query_args = array(
  'post_type' =&gt; array('post', 'podcast'),
      'tax_query' =&gt; array(
          'relation' =&gt; 'OR',
          array(
              'taxonomy' =&gt; 'series',
              'term' =&gt; 'video-blogs'
          ),
          array(
              'taxonomy' =&gt; 'category',
          ),
      ),
  'post_status' =&gt; 'publish',
  'posts_per_page' =&gt; 4,
      'orderby' =&gt; 'date',
      'order' =&gt; 'DESC'
  );
  </code></pre>
  
  <p>But it keeps triggering an error "Notice: Trying to get property of non-object".</p>
  
  <p>If I pull the 'tax_query' out it works as expected, pulling in all posts from both post and podcast post-types but I can't find a way to make the selection I'm after.</p>
  
  <p>Any ideas? Thanks in advance!</p>