[Solved] how to set a require for a string to not be null

Prachi Asks: how to set a require for a string to not be null
I want to write a require condition for string that string variable could not be null. How to write because string is not taking the != operator

Code:
function createOrder(address _seller, string memory orderName) public onlySeller returns(bool){
        require(_seller != address(0), "Invalid Address");
        require(orderName != "null", "Invalid Name");

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