title: WordPress: Exclude posts with meta_query - Not every posts has the meta_field
body: <p>I want to exclude every post with a specific value of a custom meta field.
  The problem is, that not every posts has this meta field.</p>
  
  <p>My code looks like this (excerpt of the working loop):</p>
  
  <pre><code>// WP_Query arguments
          $args = array (
              'post_parent'   =&gt; $parentid,
              'orderby'       =&gt; 'menu_order',
              'order'         =&gt; 'ASC',
              'post_type'     =&gt; array( 'page' ),
              'meta_query' =&gt; array(
                  array(
                      'key' =&gt; 'hide',
                      'value' =&gt; 1,
                      'compare' =&gt; '!='
                  )
              )
          );
  </code></pre>
  
  <p>Not every posts uses the field "hide". Some posts giving back a NULL.
  So I think, the loop isn't working because of that?!</p>
  
  <p>Is this correct? Is it necessary that every posts has a value for that key?</p>