Set or Map issue

Question

Explain an error in code below:

List<User> userList = [select id from User limit 1];

Set<User> usrs = new Set<User>();
usrs.add(userList[0]);

Map<Id, User> usrMap = new Map<Id, User>(usrs);
Set<Id> usrIds = usrMap.keySet();

It just gives me

An internal error occurred during: "Execute-Anonymous". java.lang.NullPointerException

I worked with real code which has a lot of maps of sets (Map<Id, Map<Id, User>>), I'm passing them around my methods. I encountered this Set problem in Batch class. I thought it was old Batch file problem when you can't create it normally or edit. But it seems it's a Set problem. Hm... It seems it's a Map problem. I'm passing Set of users, but Map class doesn't have constructor with Set parameter. However, SFDC doesn't tell me anything about this. It just fires an internal error.

Why doesn't Salesforce tell me anything normal about Map constructor?

Answer 1

It appears to be a problem with the Apex compiler. It isn't rejecting the Set as an invalid parameter to the Map constructor (as per Lance's answer).

Note that you can't explicitly cast between Set, List and Map or perform an instanceOf check between them. Doing so gives a compiler error like:

Incompatible types since an instance of SET is never an instance of LIST

You can simplify reproducing the problem down to:

Set<User> usrs = new Set<User>();
Map<Id, User> usrMap = new Map<Id, User>(usrs);

In my case using anonymous Apex against API v31.0 I get the message:

UNKNOWN_EXCEPTION: An unexpected error occurred. Please include this ErrorId if you contact support: 1535046690-155909 (-120809640)

The same code against the developer console causes it to hang on Executing > Sending Request > Unpacking results for me.

Depending on your support level you can either raise this directly as a bug from your Org or via the developer forums.

In the short term, convert your Sets to Lists before using them in the Maps constructor. You will need to use the List.addAll method for this.

Answer 2

According to the document, the constructor of a map should take list as parameter, not set. Probably you can try with it. Link: map constructors