title: WordPress Plugin - Checkbox Undefined Index if not checked
body: <p>I have a checkbox and if is not checked it shows "undefined index"
  I have searched here I found some similar answers but I couldn't make it work.</p>
  
  <p>Here is the way I print the checkbox input</p>
  
  <pre><code>printf(
          '&lt;input type="checkbox" id="custom_conversion_enable" name="conversion_settings_option_custom[custom_conversion_enable]" value="1" '. checked( 1, $this-&gt;options_custom['custom_conversion_enable'], false ) .' /&gt;',
                isset( $this-&gt;options_custom['custom_conversion_enable'] ) ? esc_attr( $this-&gt;options_custom['custom_conversion_enable']) : ''
  
  
         );
  </code></pre>