title: How to set query criteria to select all when combobox is left empty
body: <p>I have been trying to use <code>combobox's</code> value as a criteria for a selection query. I want it to select all options when combobox is left empty.</p>
  
  <p>I have tried to use <code>isNull</code> and <code>isEmpty</code> functions with <code>IIF</code> but the result is always empty rows.</p>
  
  <pre class="lang-sql prettyprint-override"><code>IIf(IsNull([Forms]![ReportOpener]![EnteredYear])=True;[Forms]![ReportOpener]![EnteredYear] Like "*")
  </code></pre>
  
  <pre class="lang-sql prettyprint-override"><code>IIf(IsEmpty([Forms]![ReportOpener]![EnteredYear])=True;[Forms]![ReportOpener]![EnteredYear] Like "*")
  </code></pre>