android: make response handler arguments non-optional (#395)

Description: these fields should not be optional. The callbacks must send up that data.
Risk Level: low
Testing: tested with e2e demo

Signed-off-by: Jose Nino <jnino@lyft.com>
Signed-off-by: JP Simard <jp@jpsim.com>

mobile/library/kotlin/src/io/envoyproxy/envoymobile/ResponseHandler.kt

@@ -16,12 +16,12 @@ class ResponseHandler(val executor: Executor) {
 
  override fun getExecutor(): Executor = responseHandler.executor
 
- override fun onHeaders(headers: Map<String, List<String>>?, endStream: Boolean) {
+ override fun onHeaders(headers: Map<String, List<String>>, endStream: Boolean) {
  val statusCode = headers!![":status"]?.first()?.toIntOrNull() ?: 0
  responseHandler.onHeadersClosure(headers, statusCode, endStream)
  }
 
- override fun onData(byteBuffer: ByteBuffer?, endStream: Boolean) {
+ override fun onData(byteBuffer: ByteBuffer, endStream: Boolean) {
  responseHandler.onDataClosure(byteBuffer, endStream)
  }
 
@@ -45,7 +45,7 @@ class ResponseHandler(val executor: Executor) {
  internal val underlyingObserver = EnvoyObserverAdapter(this)
 
  private var onHeadersClosure: (headers: Map<String, List<String>>, statusCode: Int, endStream: Boolean) -> Unit = { _, _, _ -> Unit }
- private var onDataClosure: (byteBuffer: ByteBuffer?, endStream: Boolean) -> Unit = { _, _ -> Unit }
+ private var onDataClosure: (byteBuffer: ByteBuffer, endStream: Boolean) -> Unit = { _, _ -> Unit }
  private var onMetadataClosure: (metadata: Map<String, List<String>>) -> Unit = { Unit }
  private var onTrailersClosure: (trailers: Map<String, List<String>>) -> Unit = { Unit }
  private var onErrorClosure: () -> Unit = { Unit }
@@ -72,7 +72,7 @@ class ResponseHandler(val executor: Executor) {
  * and flag indicating if the stream is complete.
  * @return ResponseHandler, this ResponseHandler.
  */
- fun onData(closure: (byteBuffer: ByteBuffer?, endStream: Boolean) -> Unit): ResponseHandler {
+ fun onData(closure: (byteBuffer: ByteBuffer, endStream: Boolean) -> Unit): ResponseHandler {
  this.onDataClosure = closure
  return this
  }