Revert "Do not use len() without comparison to determine if a sequence is empty"

This reverts commit ac49254.

FOR TESTING PURPOSES

Author: DimitriPapadopoulos

xarray/computation/fit.py

@@ -474,7 +474,7 @@ def _wrapper(Y, *args, **kwargs):
             mask = np.all([np.any(~np.isnan(x), axis=0), ~np.isnan(y)], axis=0)
             x = x[:, mask]
             y = y[mask]
-            if y.size == 0:
+            if not len(y):
                 popt = np.full([n_params], np.nan)
                 pcov = np.full([n_params, n_params], np.nan)
                 return popt, pcov

xarray/core/coordinates.py

@@ -549,7 +549,7 @@ def merge(self, other: Mapping[Any, Any] | None) -> Dataset:
         """
         from xarray.core.dataset import Dataset
 
-        if not other:
+        if other is None:
             return self.to_dataset()
 
         if not isinstance(other, Coordinates):
@@ -567,7 +567,7 @@ def __setitem__(self, key: Hashable, value: Any) -> None:
     def update(self, other: Mapping[Any, Any]) -> None:
         """Update this Coordinates variables with other coordinate variables."""
 
-        if not other:
+        if not len(other):
             return
 
         other_coords: Coordinates