Expose ASN.1 `Null` type through `rfc1902` module

CHANGES.txt

@@ -61,6 +61,7 @@ Revision 5.0.0, released 2018-10-??
 Revision 4.4.7, released 2018-11-XX
 -----------------------------------
 
+- Exposed ASN.1 `Null` type through `rfc1902` module for convenience.
 - Use `compile()` before `exec`'ing MIB modules to attach filename to
   the stack frames (ultimately shown in traceback/debugger)
 - Fixed hlapi/v3arch transport target caching to ensure transport targets

docs/source/docs/api-reference.rst

@@ -441,6 +441,20 @@ data description language. PySNMP types are derived from
 .. toctree::
    :maxdepth: 2
 
+.. _null:
+
+Null type
++++++++++
+
+.. autoclass:: pysnmp.proto.rfc1902.Null(initializer)
+   :members:
+
+.. note::
+
+   The `NULL` type actually belongs to the base ASN.1 types. It is not defined
+   in :RFC:`1902#section-2` as an SNMP type. The `Null` type is exposed through
+   `rfc1902` module just for convenience.
+
 .. _integer32:
 
 Integer32 type

pysnmp/proto/rfc1902.py

@@ -10,7 +10,32 @@ from pysnmp.proto import rfc1155, error
 
 __all__ = ['Opaque', 'TimeTicks', 'Bits', 'Integer', 'OctetString',
            'IpAddress', 'Counter64', 'Unsigned32', 'Gauge32', 'Integer32',
-           'ObjectIdentifier', 'Counter32']
+           'ObjectIdentifier', 'Counter32', 'Null']
+
+
+class Null(univ.Null):
+    """Creates an instance of SNMP Null class.
+
+    :py:class:`~pysnmp.proto.rfc1902.Null` type represents the absence
+    of value.
+
+    Parameters
+    ----------
+    initializer: str
+        Python string object. Must be an empty string.
+
+    Raises
+    ------
+        PyAsn1Error :
+            On constraint violation or bad initializer.
+
+    Examples
+    --------
+        >>> from pysnmp.proto.rfc1902 import *
+        >>> Null('')
+        Null('')
+        >>>
+    """
 
 
 class Integer32(univ.Integer):