CLN: Masking array for nan check, changing array dtype (pandas-dev#35498)

Author: alexhlim

pandas/_libs/index.pyx

@@ -270,11 +270,11 @@ cdef class IndexEngine:
             Py_ssize_t i, j, n, n_t, n_alloc
 
         self._ensure_mapping_populated()
-        if isnaobj(targets).any():
+        if targets[isnaobj(targets)].size > 0:
             new_targets = [0 if checknull(t) else t for t in targets]
             new_values = [0 if checknull(v) else v for v in self._get_index_values()]
-            targets = np.array(new_targets, dtype=object)
-            values = np.array(new_values, dtype=object)
+            targets = np.array(new_targets, dtype=targets.dtype)
+            values = np.array(new_values, dtype=self._get_index_values().dtype)
         else:
             values = np.array(self._get_index_values(), copy=False)