BUG: Series.astype is unable to handle pd.nan (pandas-dev#46377)

Author: kapiliyer

pandas/_libs/tslibs/nattype.pyx

@@ -28,7 +28,6 @@ from numpy cimport int64_t
 cnp.import_array()
 
 cimport pandas._libs.tslibs.util as util
-from pandas._libs.missing cimport C_NA
 from pandas._libs.tslibs.np_datetime cimport (
     get_datetime64_value,
     get_timedelta64_value,
@@ -1218,7 +1217,7 @@ cdef inline bint checknull_with_nat(object val):
     """
     Utility to check if a value is a nat or not.
     """
-    return val is None or util.is_nan(val) or val is c_NaT or val is C_NA
+    return val is None or util.is_nan(val) or val is c_NaT
 
 
 cdef inline bint is_dt64nat(object val):

pandas/_libs/tslibs/period.pyx

@@ -43,6 +43,7 @@ from libc.time cimport (
 import_datetime()
 
 cimport pandas._libs.tslibs.util as util
+from pandas._libs.missing cimport C_NA
 from pandas._libs.tslibs.np_datetime cimport (
     NPY_DATETIMEUNIT,
     NPY_FR_D,
@@ -1470,7 +1471,7 @@ cdef inline int64_t _extract_ordinal(object item, str freqstr, freq) except? -1:
     cdef:
         int64_t ordinal
 
-    if checknull_with_nat(item):
+    if checknull_with_nat(item) or item is C_NA:
         ordinal = NPY_NAT
     elif util.is_integer_object(item):
         if item == NPY_NAT:

pandas/_libs/tslibs/timedeltas.pyx

@@ -28,7 +28,6 @@ from cpython.datetime cimport (
 
 import_datetime()
 
-
 cimport pandas._libs.tslibs.util as util
 from pandas._libs.tslibs.base cimport ABCTimestamp
 from pandas._libs.tslibs.conversion cimport (