Replacing require.nil in api layer (#16906)

* Replacing require.nil in api layer

* Fixing some tests

* Fixing tests

* Addressing PR review comments

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/command_test.go

@@ -546,7 +546,7 @@ func TestGetCommand(t *testing.T) {
 
 		t.Run("InvalidId", func(t *testing.T) {
 			_, resp := client.GetCommandById(strings.Repeat("z", len(newCmd.Id)))
-			require.Error(t, resp.Error)
+			require.NotNil(t, resp.Error)
 		})
 	})
 	t.Run("UserWithNoPermissionForCustomCommands", func(t *testing.T) {