pan>
  <span><span class="type-var">'a</span> <span class="arrow">&#45;&gt;</span></span>
  <span class="type-var">'a</span></span></code></div></div><div class="odoc-spec"><div class="spec value" id="val-null_check" class="anchored"><a href="#val-null_check" class="anchor"></a><code><span><span class="keyword">val</span> null_check : <span><a href="../../Absint/FormalMap/index.html#type-t">Absint.FormalMap.t</a> <span class="arrow">&#45;&gt;</span></span> <span><a href="../../Absint/HilExp/index.html#type-