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

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* 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

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* use elif

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

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