Executing court can go beyond the degree - decree which is a nullity can be challenged even at the execution stage.

Jaipur Development Authority vs Radhey Shyam and others 

(1994) 4 SCC 370,

Equivalent citations: 1994 SCC (4) 370, 1994 SCALE (2)243

 Mr. Prasad has submitted that the decree which is a nullity can be challenged even at the execution stage