Resolve "Null Pointer Exception"

Closes #14 (closed)

Examples/Issue14.txt

+[S:00]
+{org:en}
+For transitions to and from National Operation (STM) the ETCS shall request, an acknowledgement by the driver..
+{/org}
+{unl}
+pur(promise(icl>modal>be,obj>uw,aoj>thing).@entry,transition(icl>change_of_state>thing,equ>passage).@pl)
+mod(transition(icl>change_of_state>thing,equ>passage).@pl,to(icl>how,com>content,obj>thing))
+mod(operation(icl>business_activity>thing).@maiuscul,national(icl>adj,ant>international).@maiuscul)
+obj(to(icl>how,com>content,obj>thing),operation(icl>business_activity>thing).@maiuscul)
+nam(operation(icl>business_activity>thing).@maiuscul,stm.@parenthesis)
+frm(to(icl>how,com>content,obj>thing),)
+aoj(promise(icl>modal>be,obj>uw,aoj>thing).@entry,etcs.@def)
+agt(request(icl>communicate>do,agt>volitional_thing,obj>thing),etcs.@def)
+obj(promise(icl>modal>be,obj>uw,aoj>thing).@entry,request(icl>communicate>do,agt>volitional_thing,obj>thing))
+cnt(promise(icl>modal>be,obj>uw,aoj>thing).@entry,acknowledgement(icl>message>thing,equ>acknowledgment).@indef)
+met(acknowledgement(icl>message>thing,equ>acknowledgment).@indef,driver(icl>operator>thing,ant>nondriver).@def)
+{/unl}
+[/S]