X-SuperObject thinks that non existent keys exists - json

Question

There's code a minimum reproducible example in my previous question. Please let me know if you want it copied here.
Basically, I noticed that this code:
if Assigned(job['Employer.Name.Normalized']) then
Memo1.Lines.Add('Employer name = ' + job['Employer.Name.Normalized'].AsString);
was adding an empty string to the memo.
Hardly surprising, as the JSON looks like this:
"Id": "POS-10",
"Employer": {
"Location": {
"CountryCode": "UK",
"Municipality": "Bradford"
}
},
"IsSelfEmployed": false,
"IsCurrent": false,
... etc
So, why does Assigned(job['Employer.Name.Normalized']) evaluate to true?
Note that Assigned(job.O['Employer'].O['Name'].O['Normalized']) gives the same result, but, AFIAK, it's just syntactic sugar as how it is written.
So, I tried random keys: Assigned(job['StackOverlow]) evaluates to true, as does Assigned(job['Why is this not false???'])
What am I doing wrongly? And how to I detect if a key actually exists in the ISuperObject which was obtained from my JSON?

Answer 1

This is working as designed.
Looking at XSuperObject's source code, it turns out that when you reference a member object or array, and that member doesn't exist, XSuperObject creates a new member. This lets users easily create new JSON documents.
To search for a member without creating it, you can use the Contains() method instead, eg:
if job.Contains('Employer') then
begin
emp := job.O['Employer'];
if emp.Contains('Name') then
begin
nam := emp.O['Name'];
if nam.Contains('Normalized') then
Memo1.Lines.Add('Employer name = ' + nam.S['Normalized']);
end;
end;