Allow writing null valued keys in JSON (#5065)

* Allow writing null valued keys in JSON

* Trigger

* Refactor keep nulls to be runtime config

* Rename option

* Rename option

Author: Jefffrey

arrow-array/src/numeric.rs

@@ -618,7 +618,6 @@ mod tests {
         let mask = 0b01010101_01010101_10101010_10101010;
         let actual = UInt16Type::mask_from_u64(mask);
         let expected = expected_mask!(i16, mask);
-        dbg!(&expected);
         let expected = m16x32::from_cast(i16x32::from_slice_unaligned(expected.as_slice()));
 
         assert_eq!(expected, actual);

arrow-json/src/lib.rs

@@ -82,7 +82,7 @@ pub type RawReader<R> = Reader<R>;
 pub type RawReaderBuilder = ReaderBuilder;
 
 pub use self::reader::{Reader, ReaderBuilder};
-pub use self::writer::{ArrayWriter, LineDelimitedWriter, Writer};
+pub use self::writer::{ArrayWriter, LineDelimitedWriter, Writer, WriterBuilder};
 use half::f16;
 use serde_json::{Number, Value};