Don't allow incorrect/null ARBITRARY dataType when building transactions via

API's POST /arbitrary call.

src/main/java/org/qora/api/resource/ArbitraryResource.java

@@ -185,11 +185,14 @@ public class ArbitraryResource {
 			)
 		}
 	)
-	@ApiErrors({ApiError.NON_PRODUCTION, ApiError.TRANSACTION_INVALID, ApiError.TRANSFORMATION_ERROR, ApiError.REPOSITORY_ISSUE})
+	@ApiErrors({ApiError.NON_PRODUCTION, ApiError.INVALID_DATA, ApiError.TRANSACTION_INVALID, ApiError.TRANSFORMATION_ERROR, ApiError.REPOSITORY_ISSUE})
 	public String createArbitrary(ArbitraryTransactionData transactionData) {
 		if (Settings.getInstance().isApiRestricted())
 			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.NON_PRODUCTION);
 
+		if (transactionData.getDataType() == null)
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_DATA);
+
 		try (final Repository repository = RepositoryManager.getRepository()) {
 			Transaction transaction = Transaction.fromData(repository, transactionData);