What is wrong with this method in java? I want implement recursion
<p>I have the following method, but I want to use recursion; however, I get an error: "missing return statement".</p>

<pre><code>static String buscar(NodoDeArbol raiz, String letra) {
    if(raiz == null) {
        aux="";
        for (int i = 0; i &lt; auxiliar.length()-1; i++) {
            aux+=auxiliar.charAt(i);
        }
        return aux;
    }
    auxiliar = buscar(raiz.izquierdo, auxiliar+= "0");
    auxiliar = buscar(raiz.derecho, auxiliar+= "1");
}
</code></pre>

<p>What should to do to fix this?</p>
