Multiple fixes

- Add custom exception for entity not being found
- Raise new exception when DN cannot be found from search
- Fix fetch method to return empty group object when search brings back
  no results, but preserve exception raise for multiple failed searches

mcommunity/core.py

@@ -58,7 +58,9 @@ def get_entity_dn(client, name):
             else:
                 raise MCommError('Searching MCommunity failed.')
         else:
-            raise MCommError('Unable to find "{}" in MCommunity'.format(name))
+            raise MCommEntityNotFound(
+                'Unable to find "{}" in MCommunity'.format(name)
+            )
 
     if data:
         for item in data:
@@ -82,3 +84,7 @@ def get_entity_dn(client, name):
 
 class MCommError(Exception):
     pass
+
+
+class MCommEntityNotFound(Exception):
+    pass

mcommunity/mcommunity.py

@@ -168,7 +168,10 @@ class MCommGroup:
         None
         """
 
+        try:
             self.dn = core.get_entity_dn(self.client, self.name)
+        except core.MCommEntityNotFound:
+            self.dn = None
 
         if not self.dn:
             return