Description of problem:
It gives warning, but nothing happens to the program. It continues to work properly after the warning.

Version-Release number of selected component:
pitivi-0.99-3.fc28

Additional info:
reporter:       libreport-2.9.5
cmdline:        /usr/bin/python3 /usr/bin/pitivi
crash_function: setState
exception_type: pitivi.utils.pipeline.PipelineError
executable:     /usr/bin/pitivi
interpreter:    python3-3.6.5-1.fc28.x86_64
kernel:         4.16.12-300.fc28.x86_64
runlevel:       N 5
type:           Python3
uid:            1000

Truncated backtrace:
pipeline.py:175:setState:pitivi.utils.pipeline.PipelineError: Failure changing state of the Gst.Pipeline to <enum GST_STATE_PAUSED of type Gst.State>, currently reset to NULL

Traceback (most recent call last):
  File "/usr/lib64/python3.6/site-packages/pitivi/mediafilespreviewer.py", line 218, in __asset_loaded_cb
    self._handle_new_asset(async_result=res)
  File "/usr/lib64/python3.6/site-packages/pitivi/mediafilespreviewer.py", line 211, in _handle_new_asset
    if not self._show_preview(uri, asset.get_info()):
  File "/usr/lib64/python3.6/site-packages/pitivi/mediafilespreviewer.py", line 294, in _show_preview
    self.player.setState(Gst.State.PAUSED)
  File "/usr/lib64/python3.6/site-packages/pitivi/utils/pipeline.py", line 175, in setState
    "Failure changing state of the Gst.Pipeline to %r, currently reset to NULL" % state)
pitivi.utils.pipeline.PipelineError: Failure changing state of the Gst.Pipeline to <enum GST_STATE_PAUSED of type Gst.State>, currently reset to NULL

Local variables in innermost frame:
res: <enum GST_STATE_CHANGE_FAILURE of type Gst.StateChangeReturn>
timeout: 5
cstate: <enum GST_STATE_NULL of type Gst.State>
state: <enum GST_STATE_PAUSED of type Gst.State>
self: <pipeline.AssetPipeline object at 0x7f0c34079948 (pitivi+utils+pipeline+AssetPipeline at 0x55e484eaa740)>