NullPointerException in Delegation Code

I have solved my issue changing the java delegate code in the if

	if ( office != null) 
	    {
		if (office.equals("DIPENDENTI"))
		execution.setVariable("approvatore1", "responsabile1");
		
		else if (office.equals("DAC"))
			execution.setVariable("approvatore1", "paolorossi");
		else 
		execution.setVariable("approvatore1", "giuseppeverdi");
		
       }