Null Pointer Exception

Sur unltools version b7e9329d

Exception in thread "main" java.lang.NullPointerException
        at fr.tetras_libre.unltools.unl.print.dotFile.DotFileBuilder.InternalWrite(DotFileBuilder.java:46)
        at fr.tetras_libre.unltools.unl.print.dotFile.DotFileBuilder.write(DotFileBuilder.java:28)
        at fr.tetras_libre.unltools.unl.print.dotFile.DotFileBuilder.write(DotFileBuilder.java:196)
        at unl2rdf.Unl2Rdf.runProgram(Unl2Rdf.java:43)
        at unl2rdf.Unl2Rdf.main(Unl2Rdf.java:25)

En générant le dot de:

[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]