Do not return empty entries from state_queryStorage (#2906)

* do not return empty entries from state_queryStorage

* revert back None -> null change

* Revert "revert back None -> null change"

This reverts commit 318eb043e03b7aabbc3f176e02c15fd4595d16db.

substrate/core/test-runtime/src/system.rs

@@ -238,6 +238,7 @@ fn execute_transaction_backend(utx: &Extrinsic) -> ApplyResult {
 		Extrinsic::Transfer(ref transfer, _) => execute_transfer_backend(transfer),
 		Extrinsic::AuthoritiesChange(ref new_auth) => execute_new_authorities_backend(new_auth),
 		Extrinsic::IncludeData(_) => Ok(ApplyOutcome::Success),
+		Extrinsic::StorageChange(key, value) => execute_storage_change(key, value.as_ref().map(|v| &**v)),
 	}
 }
 
@@ -273,6 +274,14 @@ fn execute_new_authorities_backend(new_authorities: &[AuthorityId]) -> ApplyResu
 	Ok(ApplyOutcome::Success)
 }
 
+fn execute_storage_change(key: &[u8], value: Option<&[u8]>) -> ApplyResult {
+	match value {
+		Some(value) => storage::unhashed::put_raw(key, value),
+		None => storage::unhashed::kill(key),
+	}
+	Ok(ApplyOutcome::Success)
+}
+
 #[cfg(feature = "std")]
 fn info_expect_equal_hash(given: &Hash, expected: &Hash) {
 	use primitives::hexdisplay::HexDisplay;