Fix exception on Transitions tab of a workflow node

Uncaught exception: com.google.gwt.event.shared.UmbrellaException: One or more exceptions caught, see full set in UmbrellaException#getCauses
    at Unknown.anonymous(Unknown Source)
    ...
    at Unknown.anonymous(Unknown Source)
Caused by: com.google.gwt.event.shared.UmbrellaException: One or more exceptions caught, see full set in UmbrellaException#getCauses
    at Unknown.anonymous(Unknown Source)
    ...
    at Unknown.anonymous(Unknown Source)
Caused by: com.google.gwt.core.client.JavaScriptException: (TypeError): a is null
 stack: W7b@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:5866
X7b@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:7334
R0d@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8304
Y0d@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8434
Ntc@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:5368
guc@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8410
hy@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8395
pz@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8016
cz@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:7519
jyb@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:4333
tyb@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8398
iy@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:6049
BTb@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8404
NMb@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8401
hy@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8395
pz@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8016
cz@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:7519
jyb@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:4333
tyb@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8398
iy@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:6049
ZSb@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:7567
$Sb@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:6845
iTb@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8404
Pnb@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:6500
Fpb/ypb<@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:8351
dk@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:4936
gk@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:7664
fk/<@https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html:6299

 fileName: https://connect.nuxeo.com/nuxeo/site/studio/ide/studio/90483DDDD959BE63A779940E8D60CB42.cache.html
 lineNumber: 5866
 columnNumber: 24
    at Unknown.anonymous(Unknown Source)