dotplot cannot set gene_symbols

I would like to change the var name when plotting dotplot by setting the gene_symbols to the desired name. But this generates the NameError. Below is an example using the scanpy built-in dataset.

adata = sc.datasets.pbmc68k_reduced()
ax = sc.pl.dotplot(adata, 'C1QA', groupby=['bulk_labels'], swap_axes=False, gene_symbols='TEST')

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-45-206578ef4fd5> in <module>
      1 adata = sc.datasets.pbmc68k_reduced()
----> 2 ax = sc.pl.dotplot(adata, 'C1QA', groupby=['bulk_labels'], swap_axes=False, gene_symbols='TEST')
      3 

~/anaconda3/envs/scRNA/lib/python3.6/site-packages/scanpy/plotting/_dotplot.py in dotplot(adata, var_names, groupby, use_raw, log, num_categories, expression_cutoff, mean_only_expressed, cmap, dot_max, dot_min, standard_scale, smallest_dot, title, colorbar_title, size_title, figsize, dendrogram, gene_symbols, var_group_positions, var_group_labels, var_group_rotation, layer, swap_axes, dot_color_df, show, save, ax, return_fig, **kwds)
    930         dot_color_df=dot_color_df,
    931         ax=ax,
--> 932         **kwds,
    933     )
    934 

~/anaconda3/envs/scRNA/lib/python3.6/site-packages/scanpy/plotting/_dotplot.py in __init__(self, adata, var_names, groupby, use_raw, log, num_categories, categories_order, title, figsize, gene_symbols, var_group_positions, var_group_labels, var_group_rotation, layer, expression_cutoff, mean_only_expressed, standard_scale, dot_color_df, dot_size_df, ax, **kwds)
    142             layer=layer,
    143             ax=ax,
--> 144             **kwds,
    145         )
    146 

~/anaconda3/envs/scRNA/lib/python3.6/site-packages/scanpy/plotting/_baseplot_class.py in __init__(self, adata, var_names, groupby, use_raw, log, num_categories, categories_order, title, figsize, gene_symbols, var_group_positions, var_group_labels, var_group_rotation, layer, ax, **kwds)
    111             num_categories,
    112             layer=layer,
--> 113             gene_symbols=gene_symbols,
    114         )
    115 

~/anaconda3/envs/scRNA/lib/python3.6/site-packages/scanpy/plotting/_anndata.py in _prepare_dataframe(adata, var_names, groupby, use_raw, log, num_categories, layer, gene_symbols)
   1837         # translate the column names to the symbol names
   1838         obs_tidy.rename(
-> 1839             columns={var_names[x]: symbols[x] for x in range(len(var_names))},
   1840             inplace=True,
   1841         )

~/anaconda3/envs/scRNA/lib/python3.6/site-packages/scanpy/plotting/_anndata.py in <dictcomp>(.0)
   1837         # translate the column names to the symbol names
   1838         obs_tidy.rename(
-> 1839             columns={var_names[x]: symbols[x] for x in range(len(var_names))},
   1840             inplace=True,
   1841         )

NameError: free variable 'symbols' referenced before assignment in enclosing scope

Versions

Reproduce the example with scanpy.pl.dotplot and trace the gene_symbols handling through plotting/_dotplot.py, plotting/_baseplot_class.py, and plotting/_anndata.py. Verify that the call no longer raises the reported NameError and that the requested gene symbol is used for the plotted label.