Morpheme.split method returns empty list

[mh-northlander]

Morpheme.split method seems returns empty morpheme list when the morpheme does not has split information.
It should return a list contains itself in that case.

reproduce:

tok = sudachipy.Dictionary().create()

ms = tok.tokenize("国会議事堂前駅で降りる")
[m.split(mode="a") for m in ms]

outputs:

[<MorphemeList[
  <Morpheme(国会, 0:2, (0, 364210))>,
  <Morpheme(議事, 2:4, (0, 686966))>,
  <Morpheme(堂, 4:5, (0, 368464))>,
  <Morpheme(前, 5:6, (0, 318425))>,
  <Morpheme(駅, 6:7, (0, 755333))>,
]>, <MorphemeList[
]>, <MorphemeList[
]>]

should be:

[<MorphemeList[
  <Morpheme(国会, 0:2, (0, 364210))>,
  <Morpheme(議事, 2:4, (0, 686966))>,
  <Morpheme(堂, 4:5, (0, 368464))>,
  <Morpheme(前, 5:6, (0, 318425))>,
  <Morpheme(駅, 6:7, (0, 755333))>,
]>, <MorphemeList[
  <Morpheme(で, ...)>,
]>, <MorphemeList[
  <Morpheme(降りる, ...)>,
]>]