 Code is buggy! Add test cases to identify which inputs are mishandled</span>
<span class="n">string</span> <span class="nf">lettersOnly</span><span class="p">(</span><span class="n">string</span> <span class="n">s</span><span class="p">)</span> <span class="p">{</span>
    <span class="n">string</span> <span class="n">result</span> <span class="o">=</span> <span class="n">charToString</span><span class="p">(</span><span class="n">s</span><span class="p">[</span><span class="mi">0</span><span class="p">]);<