ing</span> <span class="identifier">file_name</span><span class="special">;</span>
        <span class="keyword">if</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&gt;</span> <span class="identifier">param</span> <span class="special">=</span> <span cla