Skip null user objects when getting collaborators

services/web/app/coffee/Features/Collaborators/CollaboratorsHandler.coffee

@@ -30,12 +30,17 @@ module.exports = CollaboratorsHandler =
 	getMembersWithPrivilegeLevels: (project_id, callback = (error, members) ->) ->
 		CollaboratorsHandler.getMemberIdsWithPrivilegeLevels project_id, (error, members = []) ->
 			return callback(error) if error?
+			result = []
 			async.mapLimit members, 3,
 				(member, cb) ->
 					UserGetter.getUser member.id, (error, user) ->
 						return cb(error) if error?
-						return cb(null, { user: user, privilegeLevel: member.privilegeLevel })
-				callback
+						if user?
+							result.push { user: user, privilegeLevel: member.privilegeLevel }
+						cb()
+				(error) ->
+					return callback(error) if error?
+					callback null, result
 	
 	getMemberIdPrivilegeLevel: (user_id, project_id, callback = (error, privilegeLevel) ->) ->
 		# In future if the schema changes and getting all member ids is more expensive (multiple documents)

services/web/test/UnitTests/coffee/Collaborators/CollaboratorsHandlerTests.coffee

@@ -77,17 +77,19 @@ describe "CollaboratorsHandler", ->
 				{ id: "read-only-ref-2", privilegeLevel: "readOnly" }
 				{ id: "read-write-ref-1", privilegeLevel: "readAndWrite" }
 				{ id: "read-write-ref-2", privilegeLevel: "readAndWrite" }
+				{ id: "doesnt-exist", privilegeLevel: "readAndWrite" }
 			])
 			@UserGetter.getUser = sinon.stub()
 			@UserGetter.getUser.withArgs("read-only-ref-1").yields(null, { _id: "read-only-ref-1" })
 			@UserGetter.getUser.withArgs("read-only-ref-2").yields(null, { _id: "read-only-ref-2" })
 			@UserGetter.getUser.withArgs("read-write-ref-1").yields(null, { _id: "read-write-ref-1" })
 			@UserGetter.getUser.withArgs("read-write-ref-2").yields(null, { _id: "read-write-ref-2" })
+			@UserGetter.getUser.withArgs("doesnt-exist").yields(null, null)
 			@CollaboratorHandler.getMembersWithPrivilegeLevels @project_id, @callback
 		
 		it "should return an array of members with their privilege levels", ->
 			@callback
-				.calledWith(undefined, [
+				.calledWith(null, [
 					{ user: { _id: "read-only-ref-1" }, privilegeLevel: "readOnly" }
 					{ user: { _id: "read-only-ref-2" }, privilegeLevel: "readOnly" }
 					{ user: { _id: "read-write-ref-1" }, privilegeLevel: "readAndWrite" }