Fix NullReferenceExceptions during serialization

[j82w]

Pull Request Template

Description

This fixes observed null reference exceptions during serialization which seems to be caused by some race condition with the custom settings. To avoid this a new JsonSerializer is created for each call.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Closing issues

Put closes #1079

[kirankumarkolli]

We found no issue when it was the default serializer so it does not create a new instance for each call to avoid the garbage collection overhead

Is this validated or an assumption?

[j82w]

lt serializer so it does not create a new instance for each call to avoid the garbage collection overhead

All the stack traces are from custom converters path, and the default serializer doesn't have any so it shouldn't be an issue. So it's an assumption.

[kirankumarkolli]

Micro benchmark showed below

Benchmark:
Thread safe is current implementation
InstanceImpl is when serializer is created for each serialization/de-serialization invocation.

Method	Mean	Error	StdDev	StdErr	Median	Min	Q1	Q3	Max	Op/s	Gen 0	Gen 1	Gen 2	Allocated
ThreadSafeImpl	7.096 us	0.0453 us	0.2216 us	0.0136 us	7.084 us	6.638 us	6.934 us	7.222 us	7.856 us	140,933.6	3.1433	-	-	12.88 KB
InstnaceImpl	7.434 us	0.0963 us	0.4817 us	0.0289 us	7.300 us	6.761 us	7.102 us	7.565 us	9.171 us	134,518.7	3.2501	-	-	13.31 KB