Fix docstring, use checknull, closes pandas-dev#32206

Author: jbrockmendel

pandas/_libs/hashtable_class_helper.pxi.in

@@ -1228,9 +1228,7 @@ cdef class PyObjectHashTable(HashTable):
             hash(val)
 
             if ignore_na and (
-                (val is C_NA)
-                or (val != val)
-                or (val is None)
+                checknull(val)
                 or (use_na_value and val == na_value)
             ):
                 # if missing values do not count as unique values (i.e. if

pandas/core/construction.py

@@ -388,10 +388,9 @@ def extract_array(
     ----------
     obj : object
         For Series / Index, the underlying ExtensionArray is unboxed.
-        For Numpy-backed ExtensionArrays, the ndarray is extracted.
 
     extract_numpy : bool, default False
-        Whether to extract the ndarray from a PandasArray
+        Whether to extract the ndarray from a PandasArray.
 
     extract_range : bool, default False
         If we have a RangeIndex, return range._values if True