Add support for null values in template lookups

docs/en/04_Changelogs/5.0.0.md

@@ -16,7 +16,7 @@ guide developers in preparing existing 4.x code for compatibility with 5.0.
 * `<% loop %>` and `<% with %>` now only ever result in one new scope level. For example
   `<% loop $Pages.Limit(5) %>{$Up.Up.Title}<% end_loop %>` must be rewritten to use just one `$Up` statement to reach
   the parent scope.
-* Numeric and boolean values passed to methods in templates will now preserve their type, rather than
+* Numeric, boolean and null values passed to methods in templates will now preserve their type, rather than
   always being cast to strings. E.g. `$Foo(true)` would previously pass a string argument `'true'` to
   “Foo”, but will now pass an actual boolean.
 

src/View/SSTemplateParser.peg

@@ -406,9 +406,13 @@ class SSTemplateParser extends Parser implements TemplateParser
 
     QuotedString: q:/['"]/   String:/ (\\\\ | \\. | [^$q\\])* /   '$q'
 
+    # Null
+
+    Null: / (null)\b /i
+
     # Booleans
 
-    Boolean: / (true|false) /i
+    Boolean: / (true|false)\b  /i
 
     # Integers and floats
 
@@ -438,6 +442,7 @@ class SSTemplateParser extends Parser implements TemplateParser
     Argument:
         :DollarMarkedLookup |
         :QuotedString |
+        :Null |
         :Boolean |
         :IntegerOrFloat |
         :Lookup !(< FreeString)|
@@ -470,6 +475,12 @@ class SSTemplateParser extends Parser implements TemplateParser
         $res['php'] = "'" . str_replace("'", "\\'", $sub['String']['text']) . "'";
     }
 
+    function Argument_Null(&$res, $sub)
+    {
+        $res['ArgumentMode'] = 'string';
+        $res['php'] = $sub['text'];
+    }
+
     function Argument_Boolean(&$res, $sub)
     {
         $res['ArgumentMode'] = 'string';