MXS-2106: Add test case

Added a test case that reproduces the problem and verifies that it is
solved.

maxscale-system-test/CMakeLists.txt

@@ -984,6 +984,9 @@ add_test_executable(mxs2111_auth_string.cpp mxs2111_auth_string replication LABE
 # MXS-2115: Automatic version_string detection
 add_test_executable(mxs2115_version_string.cpp mxs2115_version_string replication LABELS REPL_BACKEND)
 
+# MXS-2106: NULL values with avrorouter
+add_test_executable(mxs2106_avro_null.cpp mxs2106_avro_null avro LABELS avrorouter REPL_BACKEND)
+
 configure_file(templates.h.in templates.h @ONLY)
 
 include(CTest)

maxscale-system-test/mxs2106_avro_null.cpp

@@ -0,0 +1,76 @@
+/**
+ * MXS-2106: Maxscale CDC JSON output does not respect null values
+ */
+
+#include "testconnections.h"
+#include <cdc_connector.h>
+
+int main(int argc, char** argv)
+{
+    TestConnections::skip_maxscale_start(true);
+    TestConnections::check_nodes(false);
+    TestConnections test(argc, argv);
+
+    test.set_timeout(120);
+    test.replicate_from_master(0);
+
+    test.repl->connect();
+    execute_query(test.repl->nodes[0],
+                  "CREATE OR REPLACE TABLE `test`.`test1` ("
+                  "  `test1_id` int(10) unsigned NOT NULL AUTO_INCREMENT,"
+                  "  `some_id` int(10) unsigned DEFAULT NULL,"
+                  "  `desc` varchar(50) DEFAULT NULL,"
+                  "  `some_date` timestamp NULL DEFAULT NULL,"
+                  "  `updated` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,"
+                  "  PRIMARY KEY (`test1_id`)"
+                  ") ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;"
+                  "INSERT INTO test.test1(some_id,`desc`,some_date) VALUES (1,NULL,NULL), (NULL,'value1',NULL),"
+                  "(NULL,NULL,NOW());"
+                  "UPDATE test.test1 SET some_id = NULL, `desc` = 'value2', some_date = NOW() WHERE test1_id = 1;"
+                  "UPDATE test.test1 SET some_id = 35, `desc` = NULL, some_date = NULL WHERE test1_id = 2;");
+
+    /** Give avrorouter some time to process the events */
+    test.stop_timeout();
+    sleep(10);
+    test.set_timeout(120);
+
+    CDC::Connection conn(test.maxscales->IP[0], 4001, "skysql", "skysql");
+
+    test.expect(conn.connect("test.test1"), "Failed to connect");
+
+    auto check = [&](const std::string& name) {
+            static int i = 1;
+            CDC::SRow row = conn.read();
+
+            if (row)
+            {
+                test.expect(row->is_null(name),
+                            "%d: `%s` is not null: %s",
+                            i++,
+                            name.c_str(),
+                            row->value(name).c_str());
+            }
+            else
+            {
+                test.tprintf("Error: %s", conn.error().c_str());
+            }
+        };
+
+    // The three inserts
+    check("some_date");
+    check("some_id");
+    check("some_id");
+
+    // First update
+    check("desc");
+    check("some_id");
+
+    // Second update
+    check("some_id");
+    check("desc");
+
+    execute_query(test.repl->nodes[0], "DROP TABLE `test1`");
+    test.repl->disconnect();
+
+    return test.global_result;
+}