How to check for <null> in Swift 5 and avoid 'NSInvalidArgumentException'? - swift

Question

I'm using Swift 5.
Why does an NSInvalidArgumentException occur when responseValues["CustomerID"] == '<null>'?
Obviously the if responseValues["CustomerID"] is NSNull is not doing the trick. What check should be in place to avoid the NSInvalidArgumentException
self.api.getCustomerId(callback: { getIDResult in
if let responseValues = getIDResult["ResponseValues"] {
print("GET CUSTOMER ID RESULT")
print(responseValues)
if responseValues["CustomerID"] is NSNull { // <---- crashes here when null
print("CustomerID is null")
}
else{
print("CustomerID is NOT null")
}
}
})
Succesful result
GET CUSTOMER ID RESULT
{
CustomerID = 403254;
}
CustomerID is NOT null
Crashing result when encountering a null customer id
GET CUSTOMER ID RESULT
{
CustomerID = "<null>";
}
crashes with the following
019-11-21 12:13:16.819033-0500 MyApp[29412:4207932] -[NSNull _fastCStringContents:]: unrecognized selector sent to instance 0x7fff80615710
2019-11-21 12:13:16.820557-0500 MyApp[29412:4207932] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull _fastCStringContents:]: unrecognized selector sent to instance 0x7fff80615710'
Someone was questioning whether the value was actually null, here's some debug info on that dictionary:

Answer 1

if responseValues is a dictionary, you can do this
if let customerId = responseValues["CustomerID"] as? String
{
print(customerId)
}
else
{
print("customer id isn't available")
}
if you want to know if is null, you have to change to Codable