Exsiting Calendar Items cause Exception on first Launch

[Joe]

for DAVDroid 1.3.4-1-ose on Androdi 6.0.1, on first launch DAVDroid fails with exception of there are existing entries in the calendar.

When those calendar entries are copied to the server DAVDdroid experiences a Java Excveption and synchornization fails

To be able to use DAVDroid, all existing calendar entries must be removed

[rfc2822]

Please provide steps to reproduce, debug info and verbose logs.