I have observed unexpected behavior for isusernametaken function. When we pass a

fn! doesn't have side effects, meaning if should always return expected value. isusernametaken() is a bool, and think of passing null as divided by 0. What should happen, when your only possible return value is a number?

One of the purposes is you should be able to create users based on output of this function, if it returns false for null creating the user fails.

As @stefanh791 mentioned, use a wrapper to check for null.

For more context, from Appian common objects rule!APN_displayUser, it checks for null ahead, as I said earlier, fn! functions should have no side effects, so check for null and handle accordingly:

if(isnull(ri!user), "",
if(isusernametaken(ri!user),
user(ri!user, "firstName") & " " & user(ri!user, "lastName"),
tostring(ri!user)
))

fn! doesn't have side effects, meaning if should always return expected value. isusernametaken() is a bool, and think of passing null as divided by 0. What should happen, when your only possible return value is a number?

One of the purposes is you should be able to create users based on output of this function, if it returns false for null creating the user fails.

As @stefanh791 mentioned, use a wrapper to check for null.

For more context, from Appian common objects rule!APN_displayUser, it checks for null ahead, as I said earlier, fn! functions should have no side effects, so check for null and handle accordingly:

if(isnull(ri!user), "",
if(isusernametaken(ri!user),
user(ri!user, "firstName") & " " & user(ri!user, "lastName"),
tostring(ri!user)
))