validate integer value in mule 3 dataweave 1.0

Question

I want to validate the field value as integer and make the test value as integer. In below code if the field value is string then I am getting error. Here I need to configure like if the value is not integer then make the test value is "" .

        %dw 1.0
        %output application/json
        %var field="2312321a"
        %function isEmpty(value) (value!=null and value!="")
        ---
        {
            test: field as :number as :string {format: "###"} as :number when isEmpty(field) otherwise ""
        }

expected: eg: 123.44--> 123, 1234-> 1234, 123ab-> "", "" -> ""