diff --git a/lib/ansible/playbook/base.py b/lib/ansible/playbook/base.py
index 06681abe763..39a6559235f 100644
--- a/lib/ansible/playbook/base.py
+++ b/lib/ansible/playbook/base.py
@@ -442,7 +442,7 @@ class Base:
             new_value = [ new_value ]
 
         #return list(set(value + new_value))
-        return [i for i,_ in itertools.groupby(value + new_value)]
+        return [i for i,_ in itertools.groupby(value + new_value) if i is not None]
 
     def __getstate__(self):
         return self.serialize()
diff --git a/lib/ansible/playbook/block.py b/lib/ansible/playbook/block.py
index 3831ed76004..201e881ef4b 100644
--- a/lib/ansible/playbook/block.py
+++ b/lib/ansible/playbook/block.py
@@ -323,8 +323,9 @@ class Block(Base, Become, Conditional, Taggable):
         Override for the 'tags' getattr fetcher, used from Base.
         '''
         environment = self._attributes['environment']
-        if environment is None:
-            environment = self._get_parent_attribute('environment', extend=True)
+        parent_environment = self._get_parent_attribute('environment', extend=True)
+        if parent_environment is not None:
+            environment = self._extend_value(environment, parent_environment)
 
         return environment
 
diff --git a/lib/ansible/playbook/task.py b/lib/ansible/playbook/task.py
index 8c288fc1d4e..8a3d4c4a603 100644
--- a/lib/ansible/playbook/task.py
+++ b/lib/ansible/playbook/task.py
@@ -383,8 +383,8 @@ class Task(Base, Conditional, Taggable, Become):
         Override for the 'tags' getattr fetcher, used from Base.
         '''
         environment = self._attributes['environment']
-        if environment is None:
-            environment = self._get_parent_attribute('environment')
-
+        parent_environment = self._get_parent_attribute('environment', extend=True)
+        if parent_environment is not None:
+            environment = self._extend_value(environment, parent_environment)
         return environment