Add nullable CPE

Close #27

Author: n1nj4t4nuk1

pyvalueobjects/security/nullable_cpe.py

@@ -0,0 +1,10 @@
+from pyvalueobjects.abstract.nullablevalueobject import build_nullable
+from pyvalueobjects.security.cpe import Cpe
+
+_nullable_cls = build_nullable(Cpe)
+
+
+class NullableCpe(_nullable_cls):
+
+    def __init__(self, value: str = None):
+        super().__init__(value)