fixed case when parameter is not set and added test

Author: chernser

jdbc-v2/src/main/java/com/clickhouse/jdbc/PreparedStatementImpl.java

@@ -118,9 +118,9 @@ private String buildSQL() {
         int[] positions = parsedPreparedStatement.getParamPositions();
         for (int i = 0; i < argCount; i++) {
             int p = positions[i] + posOffset;
-            String val = values[i].toString();
-            compiledSql.replace(p, p+1, val);
-            posOffset += val.length() - 1;
+            String val = values[i];
+            compiledSql.replace(p, p+1, val == null ? "NULL" : val);
+            posOffset += val == null ? 0 : val.length() - 1;
         }
         return compiledSql.toString();
     }

jdbc-v2/src/test/java/com/clickhouse/jdbc/PreparedStatementTest.java

@@ -904,4 +904,37 @@ public void testStatementsWithDatabaseInTableIdentifier() throws Exception {
             }
         }
     }
+
+    @Test(groups = {"integration "})
+    public void testNullValues() throws Exception {
+        try (Connection conn = getJdbcConnection()) {
+            final String table = "test_null_values";
+            try (Statement stmt = conn.createStatement()) {
+                stmt.execute("DROP TABLE IF EXISTS " + table);
+                stmt.execute("CREATE TABLE " + table +
+                        "(v1 Int32, v2 Nullable(Int32)) Engine MergeTree ORDER BY ()");
+            }
+
+            try (PreparedStatement stmt = conn.prepareStatement("INSERT INTO " + table + " VALUES (?, ?)")) {
+                stmt.setInt(1, 10);
+                // do not set second value
+                assertEquals(stmt.executeUpdate(), 1);
+                stmt.setInt(1, 20);
+                stmt.setObject(2, null);
+                assertEquals(stmt.executeUpdate(), 1);
+            }
+
+            try (Statement stmt = conn.createStatement();
+                ResultSet rs = stmt.executeQuery("SELECT * FROM " + table)) {
+
+                int count = 0;
+                while(rs.next()) {
+                    count++;
+                    assertNull(rs.getObject(2));
+                }
+
+                assertEquals(count, 2);
+            }
+        }
+    }
 }