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.

Conflicts:
	lib/ansible/constants.py

The way get_config is implemented change from 1.9 to devel.  I matched my code to what was there.

CHANGELOG.md

@@ -8,6 +8,37 @@ Major Changes:
 
     - 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
+ * Introducing the new block/rescue/always directives, allow for making task blocks and introducing exception like semantics
+ * New strategy plugins, allow to control the flow of execution of tasks per play, the default will be the same as before
+ * Improved error handling, now you get much more detailed parser messages. General exception handling and display has been revamped.
+ * Task includes now get evaluated during execution, end behaviour will be the same but it now allows for more dynamic includes and options.
+ * First feature of the more dynamic includes is that with_ loops are now usable with them.
+ * callback, connection and lookup plugin APIs have changed, some will require modification to work with new version
+ * callbacks are now shipped in the active directory and don't need to be copied, just whitelisted in ansible.cfg
+ * Many API changes, this will break those currently using it directly, but the new API is much easier to use and test
+ * Settings are now more inheritable, what you set at play, block or role will be automatically inhertited by the contained.
+   This allows for new features to automatically be settable at all levels, previously we had to manually code this
+ * Many more tests, new API makes things more testable and we took advantage of it
+ * big_ip modules now support turning off ssl certificate validation (use only for self signed)
+ * 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
+ * Consolidated code from modules using urllib2 to normalize features, TLS and SNI support
+ * Consiidated code from modules using urllib2 to normalize features, TLS and SNI support
+ * added meta: refresh_inventory to force rereading the inventory in a play
+ * 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)
+  * quantum_network (os_network)
+  * glance_image
+  * nova_compute   (os_server)
+  * quantum_floating_ip (os_floating_ip)
 
 New Modules:
 

lib/ansible/constants.py

@@ -31,7 +31,7 @@ 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:
@@ -42,6 +42,9 @@ def get_config(p, section, key, env_var, default, boolean=False, integer=False,
         return float(value)
     if value and islist:
         return [x.strip() for x in value.split(',')]
+    if value and isnone:
+        if value == "None":
+            return None
     return value
 
 def _get_config(p, section, key, env_var, default):
@@ -181,6 +184,7 @@ DEFAULT_FORCE_HANDLERS         = get_config(p, DEFAULTS, 'force_handlers', 'ANSI
 
 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/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']
 
@@ -145,6 +146,8 @@ class Templar:
                             resolved_val = self._available_vars[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)