Call a function with NULL input

Question

I have defined a DataWeave function that takes a string as input and can handle null input as well. However, when I call it with null input, I encounter a syntax error. Could anyone tell me why? Thanks in advance

code

%dw 2.0
output application/json

fun convertToISO(dateString: String): String =
    if (dateString == null or !(dateString contains "Date")) 
        "" 
    else 
        do {
            var milliseconds = (dateString[6 to -3] as Number)
            ---
            milliseconds as DateTime {unit: "milliseconds"} as String
        }

---

{
    
        testCorrect: convertToISO("/Date(1716249600000)/"),
        testWrongEmpty : convertToISO(""),

       testWrongNull : convertToISO(null)
    
   
}

Error

Do not use images for errors. Copy the text in the question using code block format. — aled
– aled, Commented Dec 3, 2024 at 11:38

aled · Accepted Answer · 2024-12-03 12:23:59Z

1

The error message is telling you that null, which is of type Null, is not a compatible value for a String. You can remove the null check in that function because it is going to fail trying to pass it a null argument.

As alternatives you could do one of these:

Add a Union type to the parameter. Example: fun convertToISO(dateString: String | Null): String
Use a separate overloaded function for the null case. Example: fun convertToISO(dateString: Null): String = ""
Remove the null from the caller. This means ensuring that the function is never called with a null value as an argument.

edited Dec 3, 2024 at 12:23

answered Dec 3, 2024 at 11:46

aled

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