hi! Sorry for such a stupid question but please help me to understand. I need to do something like this in @graph - how I can do it?

@graph
def my_graph():
  config = op1()
  if config: 
      r2 = op2(config)
      r3 = op3(r2)
      ....

for now if I return None in op1 it raises me en Error that

dagster._core.errors.DagsterTypeCheckDidNotPass:  Type check failed for step input "config"