body: In Rock Advertising Ltd. v. MWB Bus. Exchange Centres Ltd [2018] UK 24 Lord Sumption lists reasons why No Oral Modification clauses are beneficial.
  
  
  "The first is that it prevents attempts to undermine written agreements by informal means, a possibility which is open to abuse, for example in raising defences to summary judgment." at para 12. 
  
  
  I do not understand the example he gives, how does this undermine a contract?
  
  
  Thanks
  
  
  
title: How is "raising defences to summary judgment" an example of a contract being undermined that can be prevented with a NOM clause?