Don't convert nulls to strings.

This change is similar to https://github.com/ansible/ansible/pull/10465

It extends the logic there to also support none types.  Right now if you have
a '!!null' in yaml, and that var gets passed around, it will get converted to
a string.

eg. defaults/main.yml
```
ENABLE_AWESOME_FEATURE: !!null # Yaml Null
OTHER_CONFIG:
  secret1: "so_secret"
  secret2: "even_more_secret"

CONFIG:
  hostname: "some_hostname"
  features:
    awesame_feature: "{{ ENABLE_AWESOME_FEATURE}}"
  secrets: "{{ OTHER_CONFIG }}"
```

If you output `CONFIG` to json or yaml, the feature flag would get represented in the output
as a string instead of as a null, but secrets would get represented as a dictionary.  This is
a mis-match in behaviour where some "types" are retained and others are not.  This change
should fix the issue.

I also updated the template test to test for this and made the changes to v2.

Added a changelog entry.

CHANGELOG.md

@@ -5,6 +5,10 @@ Ansible Changes By Release
 
 Major Changes:
     - big_ip modules now support turning off ssl certificate validation (use only for self signed)
+ * big_ip modules now support turning off ssl certificate validation (use only for self signed)
+ * template code now retains types for bools, Numbers and nulls instead of turning them into strings
+   If you need the old behaviour, quote the value and it will get passed around as a string. In the
+   case of nulls, the output used to be an empty string.
 
     - template code now retains types for bools and Numbers instead of turning them into strings
       - If you need the old behaviour, quote the value and it will get passed around as a string

lib/ansible/utils/template.py

@@ -32,6 +32,7 @@ import pwd
 import ast
 import traceback
 from numbers import Number
+from types import NoneType
 
 from ansible.utils.string_functions import count_newlines_from_end
 from ansible.utils import to_bytes, to_unicode
@@ -343,7 +344,7 @@ def template_from_string(basedir, data, vars, fail_on_undefined=False):
                 var_name = only_one.group(1)
                 if var_name in vars:
                     resolved_val = vars[var_name]
-                    if isinstance(resolved_val, (bool, Number)):
+                    if isinstance(resolved_val, (bool, Number, NoneType)):
                         return resolved_val
 
         def my_finalize(thing):

test/integration/roles/test_template/files/foo.txt

@@ -3,6 +3,7 @@ templated_var_loaded
 {
     "bool": true, 
     "multi_part": "1Foo", 
+    "null_type": null, 
     "number": 5, 
     "string_num": "5"
 }

test/integration/roles/test_template/vars/main.yml

@@ -5,10 +5,12 @@ string_num: "5"
 bool_var: true
 part_1: 1
 part_2: "Foo"
+null_type: !!null
 
 templated_dict:
   number: "{{ number_var }}"
   string_num: "{{ string_num }}"
+  null_type: "{{ null_type }}"
   bool: "{{ bool_var }}"
   multi_part: "{{ part_1 }}{{ part_2 }}"
 

v2/ansible/template/__init__.py

@@ -33,6 +33,7 @@ from ansible.template.vars import AnsibleJ2Vars
 from ansible.utils.debug import debug
 
 from numbers import Number
+from types import NoneType
 
 __all__ = ['Templar']
 
@@ -41,7 +42,7 @@ __all__ = ['Templar']
 SINGLE_VAR = re.compile(r"^{{\s*(\w*)\s*}}$")
 
 # Primitive Types which we don't want Jinja to convert to strings.
-NON_TEMPLATED_TYPES = ( bool, Number )
+NON_TEMPLATED_TYPES = ( bool, Number, NoneType )
 
 JINJA2_OVERRIDE = '#jinja2:'
 JINJA2_ALLOWED_OVERRIDES = ['trim_blocks', 'lstrip_blocks', 'newline_sequence', 'keep_trailing_newline']