code: @Override
      public Method resolveFunction(String prefix, String localName) {
          if (this.memento == null) {
              this.memento = new FunctionMapperImpl();
          }
          Method m = this.target.resolveFunction(prefix, localName);
          if (m != null) {
              this.memento.mapFunction(prefix, localName, m);
          }
          return m;
      }
docs: /* (non-Javadoc)
  @see javax.el.FunctionMapper#resolveFunction(java.lang.String, java.lang.String)