IllegalArgumentException when adding member to private group

• Android version: 6.0.1
• Phone model: Neffos Y5L (TP801A)
• Briar version: 1.1.1 (9476782c)
• User feedback: "Crash while trying to add person to a group."

Stacktrace:

java.lang.IllegalArgumentException
        at org.briarproject.briar.privategroup.invitation.SessionParserImpl.parseCreatorSession(SessionParserImpl.java:54)
        at org.briarproject.briar.privategroup.invitation.GroupInvitationManagerImpl.isInvitationAllowed(GroupInvitationManagerImpl.java:482)
        at org.briarproject.briar.android.privategroup.creation.CreateGroupControllerImpl.isDisabled(CreateGroupControllerImpl.java:121)
        at org.briarproject.briar.android.contactselection.ContactSelectorControllerImpl.lambda$loadContacts$0$ContactSelectorControllerImpl(ContactSelectorControllerImpl.java:51)
        at org.briarproject.briar.android.contactselection.ContactSelectorControllerImpl$$Lambda$0.run(Unknown Source)
        at org.briarproject.briar.android.controller.DbControllerImpl.lambda$runOnDbThread$0$DbControllerImpl(DbControllerImpl.java:35)
        at org.briarproject.briar.android.controller.DbControllerImpl$$Lambda$0.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
        at java.lang.Thread.run(Thread.java:818)