grails domain object null check not working - grails 2.3.7 - grails

Question

I am working on grails application, where I have a Profile domain for every User. There are two ways to view and edit profile of a user -
The user clicks on the header link called Profile, so he can view his profile and edit it if needed.
The admin can view profile of any user by clicking a user link from the list of all users.
So in the first case if a user himself is checking his profile then on the controller side I am checking the user using spring security method "springSecurityService.currentUser".
While in second case, if the admin is checking the profile of a user then userInstance is passed to the controller action.
Problem arises when I am using it for the first case, i.e. User himself is checking his profile. Here when I check for null of userInstance parameter using if/else condition, the userInstance passes null check even though it is null. And when I print it on console it gives me a null pointer exception.
Code is-
def show(User userInstance){
println("Inside show action of profileController")
println("userInstance: " + userInstance) //Output- userInstance: null
if(userInstance != null){
println("userInstance: " + userInstance) //Output- userInstance: null
}else{
println("userInstance is null") //It never prints even though userInstance is null
userInstance = springSecurityService.currentUser
}
//More functionality to come
}
So basically its very basic thing but I am not able to figure it out, why is it not checking for null but sill printing as null.

Answer 1

when I check for null of userInstance parameter using if/else condition, the userInstance passes null check even though it is null.
This implies a pretty fundamental bug in the Groovy compiler, which I doubt. Try this instead:
def show(User userInstance){
userInstance = userInstance ?: springSecurityService.currentUser
}
Presumably when an admin is viewing a user's profile, the ID of the user is passed as a request parameter? If so, what's to stop a malicious user who knows (or guesses) the ID of another user, from accessing their profile?

Answer 2

Use this approach : Forget about isNull function but , and also forget about userIntance == null statement and try this !userInstance ,it works as follow!!!
Example
var user = User.get(10);
According to you :
def show(User userInstance){
println("Inside show action of profileController")
println("userInstance: " + userInstance) //Output- userInstance: null
if(!userInstance){
println("userInstance: " + userInstance) //Output- userInstance: null
}else{
println("userInstance is null") //It never prints even though userInstance is null
userInstance = springSecurityService.currentUser
}
//More functionality to come
}
Check this groovy script example on groovy Console Here