Functioncan't use Branch node

hello,yesterday i meet a problem about collapse to function in blueprint,
flow is that : when i press right mouse ,i’ll get a state bool value “True”,then goto branch node ,if true,i’ll emission lasers and judge whether has hit a monster;if false, do nothing. in EvevtGraph,the false node can be null,but in Function,can’t be null,must return something like true node. then… cause a very serious problem: i don’t press right mouse,but still can emission lasers,no,no,no … i don’t want to use Branch’s false node ,i only want a true node enough.

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who can help me…