Not an issue

It seems to be nullptr as list.
Try to check this
If (!list) return "nullptr";

I have two responses like this:
"Expected: equal to Vader soid: No, I am your fother!
Actual: Vader soid: No, I am your father!"
But there is no "equal to..." text in test example.
Maybe someone hit the same?

bad thing is i do not see any debug from doing std::cout
But the code is running and if i change it, i will receive
what it expected isntead.
But no result from std::cout

I think you should make the Instruction more clear by saying the last element will be Null(in java) or null (in C)
but you stated it like file system structure Null/null/NULL.

Another Important thing Stated clear that NULL will be in as a word not like "" or " ".

Thanks

Perhaps you tried to access an array element using an out-of-range index or accessing a nonexistent property on an object? If you #include <iostream> on the top of your solution file and print out all the intermediate results to the console it could certainly help you identify the bug in your code, cheers :)

Signal:
Process exited prematurely with a SIGSEGV signal.

How should it be handled?

Help us help you. What language ?!?

How can my program possibly work properly with 23 and -7 pair, with -45 and -54 pair,
BUT not with -97 and 6 pair?

Thank you! But it is a great performance driven task.

If task was find the BIGGEST NUMBER consisting of the same digits this kata was 6 kyu. Or easier

Paste your code, mark it as spoiler so we can see what fails. As far as I've tested javascript kata version works.

It is important suggestion. I missed it!

6 characters req.

You have a problem in checking code:
[eval]:83
});
^
SyntaxError: Unexpected token )

it is about +18 lines of code from my last line. Because Ctrl + f does not even found such sequence in my code.
Please, fix it.