reverted

platform/projectModel-impl/src/com/intellij/openapi/roots/impl/ContentEntryImpl.java

@@ -270,9 +270,6 @@ public class ContentEntryImpl extends RootModelComponentBase implements ContentE
   @Override
   public ExcludeFolder addExcludeFolder(@NotNull VirtualFile file) {
     assert !isDisposed();
-    if (!file.isDirectory()) {
-      throw new IllegalArgumentException("File must be folder but got: "+file);
-    }
     assertCanAddFolder(file);
     return addExcludeFolder(new ExcludeFolderImpl(file, this));
   }