Program: 70039
Project: 70039
Buggy source:
private static Object[] findWritableRootFolderForRecursion(VFSContainer rootDir,String relFilePath,int recursionLevel){
  recursionLevel++;
  if (recursionLevel > 20) {
    log.warn("String_Node_Str" + rootDir + "String_Node_Str"+ relFilePath);
    return null;
  }
  if (rootDir instanceof NamedContainerImpl) {
    rootDir=((NamedContainerImpl)rootDir).delegate;
  }
  if (rootDir instanceof MergeSource) {
    VFSContainer rootWriteContainer=((MergeSource)rootDir).getRootWriteContainer();
    if (rootWriteContainer == null) {
      List<VFSItem> children=rootDir.getItems();
      String nextChildName=relFilePath.substring(1,relFilePath.indexOf("String_Node_Str",1));
      if (children.size() == 0) {
        return null;
      }
      for (      VFSItem child : children) {
        if (child.getName().equals(nextChildName)) {
          if (child instanceof VFSContainer) {
            rootDir=(VFSContainer)child;
            relFilePath=relFilePath.substring(relFilePath.indexOf("String_Node_Str",1));
            break;
          }
 else {
            return null;
          }
        }
      }
    }
 else {
      rootDir=rootWriteContainer;
    }
  }
  if (rootDir != null && rootDir instanceof LocalFolderImpl) {
    return new Object[]{rootDir,relFilePath};
  }
 else {
    return findWritableRootFolderForRecursion(rootDir,relFilePath,recursionLevel);
  }
}

Fixed version (ground truth):
private static ContainerAndFile findWritableRootFolderForRecursion(VFSContainer rootDir,String relFilePath,int recursionLevel){
  recursionLevel++;
  if (recursionLevel > 20) {
    log.warn("String_Node_Str" + rootDir + "String_Node_Str"+ relFilePath);
    return null;
  }
  if (rootDir instanceof NamedContainerImpl) {
    rootDir=((NamedContainerImpl)rootDir).getDelegate();
  }
  if (rootDir instanceof MergeSource) {
    MergeSource mergedDir=(MergeSource)rootDir;
    int stop=relFilePath.indexOf("String_Node_Str",1);
    if (stop > 0) {
      String nextLevel=extractChild(relFilePath);
      VFSItem item=mergedDir.resolve(nextLevel);
      if (item instanceof NamedContainerImpl) {
        item=((NamedContainerImpl)item).getDelegate();
      }
      if (item instanceof MergeSource) {
        rootDir=(MergeSource)item;
        relFilePath=relFilePath.substring(stop);
        return findWritableRootFolderForRecursion(rootDir,relFilePath,recursionLevel);
      }
    }
    VFSContainer rootWriteContainer=mergedDir.getRootWriteContainer();
    if (rootWriteContainer == null) {
      List<VFSItem> children=rootDir.getItems();
      if (children.isEmpty()) {
        return null;
      }
      String nextChildName=relFilePath.substring(1,relFilePath.indexOf("String_Node_Str",1));
      for (      VFSItem child : children) {
        if (child.getName().equals(nextChildName)) {
          if (child instanceof VFSContainer) {
            rootDir=(VFSContainer)child;
            relFilePath=relFilePath.substring(relFilePath.indexOf("String_Node_Str",1));
            break;
          }
 else {
            return null;
          }
        }
      }
    }
 else {
      rootDir=rootWriteContainer;
    }
  }
  if (rootDir != null && rootDir instanceof LocalFolderImpl) {
    return new ContainerAndFile(rootDir,relFilePath);
  }
 else {
    return findWritableRootFolderForRecursion(rootDir,relFilePath,recursionLevel);
  }
}