Cannot save as Gimp palette when there is a gradient in the document

When there's a gradient or a swatch in the document, the 'Save as Gimp palette' extension fails with the following traceback:

Traceback (most recent call last):
  File "export_gimp_palette.py", line 53, in <module>
    ExportGpl().run()
  File "/opt/inkscape_master/share/inkscape/extensions/inkex/base.py", line 88, in run
    self.save_raw(self.effect())
  File "/opt/inkscape_master/share/inkscape/extensions/inkex/base.py", line 110, in save_raw
    self.save(self.options.output)
  File "export_gimp_palette.py", line 35, in save
    colors = dict(self.walk(self.svg))
  File "export_gimp_palette.py", line 49, in walk
    for color in self.walk(child):
  File "export_gimp_palette.py", line 49, in walk
    for color in self.walk(child):
  File "export_gimp_palette.py", line 49, in walk
    for color in self.walk(child):
  File "export_gimp_palette.py", line 44, in walk
    col = inkex.Color(styles.get(tag, None))
  File "/opt/inkscape_master/share/inkscape/extensions/inkex/colors.py", line 217, in __init__
    self.append(val)
  File "/opt/inkscape_master/share/inkscape/extensions/inkex/colors.py", line 229, in append
    val = float(val)
ValueError: could not convert string to float: #lineargradient1384

(This works with 0.92.x)