Hello and welcome to Microsoft Q&A @Sampath S
As I understand your source XML has NAN (Not a number) in a float field, but your SQL isn't accepting this, and treating it as string. You want to change them to Null.
I do have an idea to try. In the XML Dataset, there is a "Null value" option. I was thinking to try with putting NAN in that field.
I don't think ADF can do that.