sc.pl.dpt error if n_branchings=0 in sc.tl.dpt

tl.dpt with no branching events works:

sc.tl.dpt(adata, n_branchings=0, n_dcs=10, min_group_size=0.01, allow_kendall_tau_shift=True)
yields
performing Diffusion Pseudotime analysis
    initialized `.distances` `.connectivities` `.eigen_values` `.eigen_basis` `.distances_dpt`
    eigenvalues of transition matrix
    [1.         0.87799305 0.74851424 0.7235198  0.5982796  0.5652917
     0.45321003 0.35327435 0.33786523 0.29598442]
    finished (0:01:09.57) --> added
    'dpt_pseudotime', the pseudotime (adata.obs)

But calling pl.dpt on this object yields an error, looking at the above outout of tl.dpt it seems that dpt_groups was not created in adata.obs if n_branchings=0?

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
/usr/local/lib/python3.6/site-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   2524             try:
-> 2525                 return self._engine.get_loc(key)
   2526             except KeyError:

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

KeyError: 'dpt_groups'

During handling of the above exception, another exception occurred:

KeyError                                  Traceback (most recent call last)
<ipython-input-102-eb7d1d859c99> in <module>()
----> 1 sc.pl.dpt(adata, groups=None)

~/gitDevelopment/scanpy/scanpy/plotting/tools/__init__.py in dpt(adata, basis, color, alpha, groups, components, projection, legend_loc, legend_fontsize, legend_fontweight, color_map, palette, right_margin, size, title, show, save)
    677     """
    678     colors = ['dpt_pseudotime']
--> 679     if len(np.unique(adata.obs['dpt_groups'].values)) > 1: colors += ['dpt_groups']
    680     if color is not None: colors = color
    681     dpt_scatter(

/usr/local/lib/python3.6/site-packages/pandas/core/frame.py in __getitem__(self, key)
   2137             return self._getitem_multilevel(key)
   2138         else:
-> 2139             return self._getitem_column(key)
   2140 
   2141     def _getitem_column(self, key):

/usr/local/lib/python3.6/site-packages/pandas/core/frame.py in _getitem_column(self, key)
   2144         # get column
   2145         if self.columns.is_unique:
-> 2146             return self._get_item_cache(key)
   2147 
   2148         # duplicate columns & possible reduce dimensionality

/usr/local/lib/python3.6/site-packages/pandas/core/generic.py in _get_item_cache(self, item)
   1840         res = cache.get(item)
   1841         if res is None:
-> 1842             values = self._data.get(item)
   1843             res = self._box_item_values(item, values)
   1844             cache[item] = res

/usr/local/lib/python3.6/site-packages/pandas/core/internals.py in get(self, item, fastpath)
   3841 
   3842             if not isna(item):
-> 3843                 loc = self.items.get_loc(item)
   3844             else:
   3845                 indexer = np.arange(len(self.items))[isna(self.items)]

/usr/local/lib/python3.6/site-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   2525                 return self._engine.get_loc(key)
   2526             except KeyError:
-> 2527                 return self._engine.get_loc(self._maybe_cast_indexer(key))
   2528 
   2529         indexer = self.get_indexer([key], method=method, tolerance=tolerance)

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

KeyError: 'dpt_groups'

scanpy==1.0.4+11.gc241098 anndata==0.5.10 numpy==1.14.2 scipy==1.0.1 pandas==0.22.0 scikit-learn==0.19.1 statsmodels==0.8.0 python-igraph==0.7.1 louvain==0.6.1

Start with scanpy/plotting/tools/init.py, especially the dpt function and its access to adata.obs['dpt_groups']. Reproduce the issue with sc.tl.dpt(..., n_branchings=0) followed by sc.pl.dpt(adata, groups=None). Done means plotting no longer raises KeyError when dpt_groups is absent.