Script working inside a trigger but breaking inside an object function, why

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I'm working on a custom object. When I run a script from a trigger it works but if I run the same code from an object function, it throws an error saying "Cannot invoke method getAttribute() on null object". The script populates a long text field with a lead's property:

 

def vo = newView('Lead')

def foundRows = vo.findByKey(key(100000222932042),1)

def foundRow = foundRows[0]

setAttribute('LongTextField_c', foundRow.getAttribute('PrimaryContactPersonLastName'))

 

Any clue about this strange behavior? How can it be surpassed?