Support nested Map transformations

[MichailKaramanos]

Currently, when encountered a nested Map the following error is given:

java.lang.IllegalArgumentException: Field 'someNestedMap' is not a struct type or an array.

Would be a nice to have improvement. Are there plans to introduce this feature?

[yruslan]

Yes, definitely we need to add support nestedMaps.

We need to investigate if we can use transform(...) on maps similarly how we use it on arrays.

Let's use this issue to track progress on this.