Prevent a list with np.nan converting to float

Author: sanggon6107

pandas/core/generic.py

@@ -9713,11 +9713,13 @@ def _where(
             cond = cond.align(self, join="right")[0]
         else:
             if not hasattr(cond, "shape"):
-                cond = np.asanyarray(cond)
+                cond = np.asanyarray(cond, dtype=object)
+            if not cond.flags.writeable:
+                cond.setflags(write=True)
+            cond[isna(cond)] = True
             if cond.shape != self.shape:
                 raise ValueError("Array conditional must be same shape as self")
             cond = self._constructor(cond, **self._construct_axes_dict(), copy=False)
-            cond = cond.fillna(True)
 
         # make sure we are boolean
         fill_value = bool(inplace)
@@ -10098,7 +10100,7 @@ def mask(
 
         # see gh-21891
         if not hasattr(cond, "__invert__"):
-            cond = np.array(cond)
+            cond = np.array(cond, dtype=object)
 
         if isinstance(cond, np.ndarray):
             if all(