1) Test coverage fixed

2) Test fixed

tests/RunCoverage.bat

@@ -33,7 +33,6 @@ exit /b %errorlevel%
 -skipautoprops ^
 -output:"%~dp0\GeneratedReports\Core.xml" ^
 -oldStyle
-exit /b %errorlevel%
 
 "%UserProfile%\.nuget\packages\OpenCover\4.6.519\tools\OpenCover.Console.exe" ^
 -register:user ^

tests/Squidex.Write.Tests/Apps/AppDomainObjectTests.cs

@@ -75,6 +75,12 @@ namespace Squidex.Write.Tests.Apps
             Assert.Throws<DomainException>(() => sut.AssignContributor(new AssignContributor { ContributorId = contributorId }));
         }
 
+        [Fact]
+        public void AssignContributor_should_throw_if_contributor_id_not_valid()
+        {
+            Assert.Throws<DomainException>(() => sut.AssignContributor(new AssignContributor()));
+        }
+
         [Fact]
         public void AssignContributor_should_throw_if_single_owner_becomes_non_owner()
         {
@@ -106,6 +112,12 @@ namespace Squidex.Write.Tests.Apps
             Assert.Throws<DomainException>(() => sut.RemoveContributor(new RemoveContributor { ContributorId = contributorId }));
         }
 
+        [Fact]
+        public void RemoveContributor_should_throw_if_contributor_id_not_valid()
+        {
+            Assert.Throws<DomainException>(() => sut.RemoveContributor(new RemoveContributor()));
+        }
+
         [Fact]
         public void RemoveContributor_should_throw_if_all_owners_removed()
         {