Initialize _base URL_ in Create Term Definition to null. For #375.

Author: gkellogg

index.html

@@ -1517,7 +1517,7 @@ <h3>Algorithm</h3>
         a <var>term</var>,
         and a map <var>defined</var>.
         <span class="changed">The optional inputs are
-          <var>base URL</var>,
+          <var>base URL</var> defaulting to <code>null</code>,
           <var>protected</var> which defaults to <code>false</code>,
           and <var>override protected</var>, defaulting to <code>false</code>,
           which is used to allow changes to protected terms.</span>.