public void setHttpActionAdapterIfUndefined(final HttpActionAdapter httpActionAdapter) {
        if (this.httpActionAdapter == null) {
            setHttpActionAdapter(httpActionAdapter);
        }
    }
<p>setHttpActionAdapterIfUndefined.</p>

@param httpActionAdapter a {@link HttpActionAdapter} object
pac4j-core/src/main/java/org/pac4j/core/config/Config.java