playbook, include: fix Unexpected Exception: 'NoneType' object has no attribute 'strip' (#15574)

If `include:` statement is used without argument, we get a traceback.

lib/ansible/playbook/playbook_include.py

@@ -135,6 +135,9 @@ class PlaybookInclude(Base, Conditional, Taggable):
         Splits the include line up into filename and parameters
         '''
 
+        if v is None:
+           raise AnsibleParserError("include parameter is missing", obj=ds)
+
         # The include line must include at least one item, which is the filename
         # to include. Anything after that should be regarded as a parameter to the include
         items = split_args(v)