Simplify chaining with null_op (refactored, M.U.)
Simplify chaining with null_op (refactored, M.U.)

mrirecon/bart,sidward/bart,mrirecon/bart,mrirecon/bart,sidward/bart,sidward/bart,sdimoudi/bart,sdimoudi/bart,mrirecon/bart,sdimoudi/bart,sdimoudi/bart,sidward/bart,sdimoudi/bart,mrirecon/bart,sidward/bart