   <body>
<code class="code"><span class="keyword">sig</span><br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;nullable_to_opt&nbsp;:&nbsp;<span class="keywordsign">'</span>a&nbsp;<span class="constructor">Js</span>.null_undefined&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="keywordsign">'</span>a&nbsp;option<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;undefined_to_opt&nbsp;:&nbsp;<span class="keywordsign">'</span>a&nbsp;<span class="constructor">Js</span>.undefined&nbsp;<spa