code: public static PyExpr genPyNullCheck(PyExpr expr) {
      ImmutableList<PyExpr> exprs = ImmutableList.of(expr, new PyExpr("None", Integer.MAX_VALUE));
      // Note: is/is not is Python's identity comparison. It's used for None checks for performance.
      String conditionalExpr = genExprWithNewToken(Operator.EQUAL, exprs, "is");
      return new PyExpr(conditionalExpr, PyExprUtils.pyPrecedenceForOperator(Operator.EQUAL));
    }
docs: Generates a Python null (None) check expression for the given {@link PyExpr}.