hp-sendfax crashes if python-reportlab is missing

$ hp-sendfax

HP Linux Imaging and Printing System (ver. 3.18.6)
PC Sendfax Utility ver. 9.0

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

warning: Reportlab not installed. Fax coverpages disabled.
warning: Please install version 2.0+ of Reportlab for coverpage support.
qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 669, resource id: 13465094, major code: 40 (TranslateCoords), minor code: 0
Traceback (most recent call last):
  File "/usr/share/hplip/ui5/sendfaxdialog.py", line 375, in FilesTable_fileListChanged
    self.toggleCoverPage(self.FilesTable.isMIMETypeInList(MIME_TYPE_COVERPAGE))
  File "/usr/share/hplip/ui5/sendfaxdialog.py", line 328, in toggleCoverPage
    self.CoverPageGroupBox.toggled[bool].disconnect(self.CoverPageGroupBox_toggled)
TypeError: 'method' object is not connected
Aborted (core dumped)