uage variable, replacing any previously assignment to the same
 variable. The assignment for the variable is removed if the expression is <code>null</code>.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>variable</code> - The variable name</dd>
<dd><code>expression</code> - The ValueExpression to be assigned to the variable.</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>The previous ValueExpression assigned to this variable, null if there is no previous assignment to