pitivi crashed with AttributeError in _create_next_thumb(): 'NoneType' object has no attribute 'seek'

A crash occurred that I was configuring rendering, but the program kept working.

ProblemType: Crash
DistroRelease: Ubuntu 18.04
Package: pitivi 0.99-2
ProcVersionSignature: Ubuntu 4.13.0-32.35-generic 4.13.13
Uname: Linux 4.13.0-32-generic x86_64
ApportVersion: 2.20.8-0ubuntu8
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sun Feb 11 18:52:39 2018
ExecutablePath: /usr/bin/pitivi
InstallationDate: Installed on 2017-11-12 (91 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Alpha amd64 (20171109)
InterpreterPath: /usr/bin/python3.6
ProcCmdline: /usr/bin/python3 /usr/bin/pitivi
Python3Details: /usr/bin/python3.6, Python 3.6.4, python3-minimal, 3.6.4-1
PythonArgs: ['/usr/bin/pitivi']
PythonDetails: /usr/bin/python2.7, Python 2.7.14+, python-minimal, 2.7.14-4
SourcePackage: pitivi
Title: pitivi crashed with AttributeError in _create_next_thumb(): 'NoneType' object has no attribute 'seek'
Traceback:
 Traceback (most recent call last):
   File "/usr/lib/x86_64-linux-gnu/pitivi/python/pitivi/timeline/previewers.py", line 556, in _create_next_thumb
     self.pipeline.seek(1.0,
 AttributeError: 'NoneType' object has no attribute 'seek'
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo