Fixes #4854 Explicitly handle nullptr in sax_parse (#4873)

* handle nullptr explicitly

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* add test

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* make amalgamate

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* Fix formatting

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* move sax parse test to relevant unit test file

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* extend exceptions.md to include other_error.502

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* Better exception messages

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* link sax_parse function

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* fix string

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* amalgamate

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* fix clang-tidy checks

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* cover valid handler with no throw

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* Add tests for other two overloads

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* cover overload with valid sax handler

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* pass an rvalue

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* ignore -Wtautological-pointer-compare

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* ignore clang-analyzer-core.NonNullParamChecker

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* ignore gcc -Wnonnull-compare

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* ignore undefined-behaviour-sanitizer

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* nest directives to ignore sanitizer errors

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

* use elif

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

---------

Signed-off-by: Nikhil <nikhilreddydev@gmail.com>

docs/mkdocs/docs/home/exceptions.md

@@ -900,3 +900,13 @@ A JSON Patch operation 'test' failed. The unsuccessful operation is also printed
     ```
     [json.exception.other_error.501] unsuccessful: {"op":"test","path":"/baz","value":"bar"}
     ```
+
+### json.exception.other_error.502
+
+This exception occurs when a null pointer is passed as SAX handler in [sax_parse](../api/basic_json/sax_parse.md) function.
+
+!!! failure "Example message"
+
+    ```
+    [json.exception.other_error.502] SAX handler must not be null
+    ```