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 specifically for the change from empty string to null as the default.

Made the null representation configurable.

It still defaults to the python NoneType but can be overriden to be an emptystring by updating
the DEFAULT_NULL_REPRESENTATION config.

CHANGELOG.md

@@ -18,6 +18,13 @@ Major Changes:
    If you need the old behaviour, quote the value and it will get passed around as a string
  * added meta: refresh_inventory to force rereading the inventory in a play
  * vars are now settable at play, block, role and task level
+ * 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. In the
+   case of nulls, the output used to be an empty string.
+ * Empty variables and variables set to null in yaml will no longer be converted to empty strings.
+   They will retain the value of `None`.  To go back to the old behaviour, you can override
+   the `null_representation` setting to an empty string in your config file or by setting the
+   `ANSIBLE_NULL_REPRESENTATION` environment variable.
 
 Deprecated Modules (new ones in parens):
   * ec2_ami_search (ec2_ami_find)

lib/ansible/constants.py

@@ -40,7 +40,7 @@ def mk_boolean(value):
     else:
         return False
 
-def get_config(p, section, key, env_var, default, boolean=False, integer=False, floating=False, islist=False):
+def get_config(p, section, key, env_var, default, boolean=False, integer=False, floating=False, islist=False, isnone=False):
     ''' return a configuration variable with casting '''
     value = _get_config(p, section, key, env_var, default)
     if boolean:
@@ -53,6 +53,9 @@ def get_config(p, section, key, env_var, default, boolean=False, integer=False,
         elif islist:
             if isinstance(value, string_types):
                 value = [x.strip() for x in value.split(',')]
+        elif isnone:
+            if value == "None":
+                value = None
         elif isinstance(value, string_types):
             value = unquote(value)
     return value
@@ -205,6 +208,7 @@ DEFAULT_LOAD_CALLBACK_PLUGINS  = get_config(p, DEFAULTS, 'bin_ansible_callbacks'
 DEFAULT_CALLBACK_WHITELIST     = get_config(p, DEFAULTS, 'callback_whitelist', 'ANSIBLE_CALLBACK_WHITELIST', [], islist=True)
 RETRY_FILES_ENABLED            = get_config(p, DEFAULTS, 'retry_files_enabled', 'ANSIBLE_RETRY_FILES_ENABLED', True, boolean=True)
 RETRY_FILES_SAVE_PATH          = get_config(p, DEFAULTS, 'retry_files_save_path', 'ANSIBLE_RETRY_FILES_SAVE_PATH', '~/')
+DEFAULT_NULL_REPRESENTATION    = get_config(p, DEFAULTS, 'null_representation', 'ANSIBLE_NULL_REPRESENTATION', None, isnone=True)
 
 # CONNECTION RELATED
 ANSIBLE_SSH_ARGS               = get_config(p, 'ssh_connection', 'ssh_args', 'ANSIBLE_SSH_ARGS', None)

lib/ansible/template/__init__.py

@@ -37,6 +37,7 @@ from ansible.template.vars import AnsibleJ2Vars
 from ansible.utils.debug import debug
 
 from numbers import Number
+from types import NoneType
 
 __all__ = ['Templar']
 
@@ -187,6 +188,8 @@ class Templar:
                             resolved_val = self._available_variables[var_name]
                             if isinstance(resolved_val, NON_TEMPLATED_TYPES):
                                 return resolved_val
+                            elif isinstance(resolved_val, NoneType):
+                                return C.DEFAULT_NULL_REPRESENTATION
 
                     result = self._do_template(variable, preserve_trailing_newlines=preserve_trailing_newlines, fail_on_undefined=fail_on_undefined, overrides=overrides)
 

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 }}"
 

v1/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):