[rules-users] Validation flow - defer expression evaluation

[peters]

putting "$var: user.?manager.name" to avoid nullpointer in the business rule 
defeats the purpose of a sanity check upfront, as execution should fail if
the relation is empty. 
Nullpointers are not an elegant way to fail, and the stack trace gives no
clue in which rule the error occurred.

I was thinking of starting a seperate session to run validation. This is
cumbersome however, en I would like to find a way to solve this problem with
a process(rule) flow. I guess it's about rule activation occuring.
Is there a way to activate the business rules only when validation rules
have passed?

I will try starting a subprocess, and see if this activates the business
rules at the appropriate time in the flow.

Any suggestions to avoid this trial and error approach are most welcome.  

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