How to catch null value on http response - groovy

Question

I have the following code method which is used to test for an existing user in MSGraph API
public String getGuestUserId(String AuthToken,String userEmail){
String _userId
def http = new HTTPBuilder(graph_base_user_url + "?")
http.request(GET) {
requestContentType = ContentType.JSON
//uri.query = [ $filter:"mail eq '$userEmail'"].toString()
uri.query=[$filter:"mail eq '$userEmail'"]
headers.'Authorization' = "Bearer " + AuthToken
response.success = { resp, json ->
//as the retunr json alue is an array collection we need to get the first element as we request all time one record from the filter
**_userId=json.value[0].id**
}
// user ID not found : error 404
response.'404' = { resp ->
_userId = 'Not Found'
}
}
_userId
}
This method works fine when the user is existing and will return properly from the success response the user ID property.
The issue I get is that if the user is not existing, the ID field is not existing either and the array is empty.
How can I handle efficiently that case and return a meaning full value to the caller like "User Does not exist"
I have try a catch exception in the response side but seems doe snot to work
Any idea how can I handle the test like if the array[0] is empty or does not contains any Id property, then return something back ?
Thanks for help
regards

Answer 1

It seems to be widely accepted practice not to catch NPE. Instead, one should check if something is null.
In your case:
You should check if json.value is not empty
You also should check if id is not null.
Please also note that handling exceptions in lambdas is always tricky.
You can change the code to:
http.request(GET) {
requestContentType = ContentType.JSON
uri.query=[$filter:"mail eq '$userEmail'"]
headers.'Authorization' = "Bearer " + AuthToken
if (json.value && json.value[0].id) {
response.success = { resp, json -> **_userId=json.value[0].id** }
} else {
// Here you can return generic error response, like the one below
// or consider more granular error reporting
response.'404' = { resp -> _userId = 'Not Found'}
}
}