yams #288556 Check constraint only if value is set [validation pending]

example :
Date(constraints=[BoundaryConstraint('<=', Attribute('end_date'))])
Only check the condition if end_date not None

prioritynormal
typebug
done in0.41.0
load1.000
load left0.000
closed by#53c8caa43cc0 handle none or unset attribute in BoundaryConstraint
patchhandle none or unset attribute in BoundaryConstraint [applied]