FutureWarning in summary_m.py

[jobrachem]

We get a FutureWarning in the Summary._error_df() method:

liesel/liesel/goose/summary_m.py:362: FutureWarning: The behavior of array concatenation with empty entries is deprecated. In a future version, this will no longer exclude empty items when determining the result dtype. To retain the old behavior, exclude the empty entries before the concat operation.
  df = pd.concat({

My assessment is that this warning comes up if there's an empty error dataframe, i.e. no errors for a kernel.