FEEL: external java function references not working for functions with variable number of parameters

{ 
    string format : function( mask, value ) external {
                      java : {
                          class : "java.lang.String",
                          method signature : "format( java.lang.String, [Ljava.lang.Object; )"
                      }
                  },
    format currency : function( amount ) 
                 string format( "$%,4.2f", amount ),
   result : format currency( 76499.3456 )
}