FileTrees switchToStrongRefs() {
    if (myRefToPsi == null) return this;

    forEachCachedPsi(psi -> {
      ASTNode node = psi.getNode();
      LOG.assertTrue(node.getPsi() == psi);
      psi.setSubstrateRef(SubstrateRef.createAstStrongRef(node));
    });

    return new FileTrees(myFile, myStub, myTreeElementPointer, null);
  }
FileTrees switchToStrongRefs()