remove some empty lines

mlair/helpers/statistics.py

@@ -225,6 +225,7 @@ def calculate_error_metrics(a, b, dim):
     n = (a - b).notnull().sum(dim)
     return {"mse": mse, "rmse": rmse, "mae": mae, "n": n}
 
+
 def skill_score_based_on_mse(data: xr.DataArray, obs_name: str, pred_name: str, ref_name: str,
                              aggregation_dim: str = "index", competitor_dim: str = "type") -> xr.DataArray:
     obs = data.sel({competitor_dim: obs_name})
@@ -234,8 +235,6 @@ def skill_score_based_on_mse(data: xr.DataArray, obs_name: str, pred_name: str,
     return ss
 
 
-
-
 def mann_whitney_u_test(data: pd.DataFrame, reference_col_name: str, **kwargs):
     """
     Calculate Mann-Whitney u-test. Uses pandas' .apply() on scipy.stats.mannwhitneyu(x, y, ...).