<bugfix>UpgradeWorkflowError tries to trim None-value</bugfix>
<bugfix>UpgradeWorkflowError tries to trim None-value</bugfix>

core/upgradeworkflow.py:
- UpgradeWorkflowError: only trim if value is not None

VisTrails/VisTrails,minesense/VisTrails,hjanime/VisTrails,minesense/VisTrails,Nikea/VisTrails,celiafish/VisTrails,Nikea/VisTrails,minesense/VisTrails,VisTrails/VisTrails,hjanime/VisTrails,celiafish/VisTrails,hjanime/VisTrails,Nikea/VisTrails,hjanime/VisTrails,minesense/VisTrails,VisTrails/VisTrails,minesense/VisTrails,VisTrails/VisTrails,celiafish/VisTrails,VisTrails/VisTrails,celiafish/VisTrails,hjanime/VisTrails,Nikea/VisTrails