[jdbc-v2] Fix NPE in ResultSetMetaDataImpl#getColumnClassName

Author: jielongping

jdbc-v2/src/main/java/com/clickhouse/jdbc/metadata/ResultSetMetaDataImpl.java

@@ -179,7 +179,11 @@ public boolean isDefinitelyWritable(int column) throws SQLException {
     @Override
     public String getColumnClassName(int column) throws SQLException {
         try {
-            return typeClassMap.getOrDefault(getColumn(column).getDataType(), Object.class).getName();
+            Class<?> columnClassType = typeClassMap.get(getColumn(column).getDataType());
+            if (columnClassType == null) {
+                columnClassType = Object.class;
+            }
+            return columnClassType.getName();
         } catch (Exception e) {
             throw ExceptionUtils.toSqlState(e);
         }

jdbc-v2/src/test/java/com/clickhouse/jdbc/metadata/ResultSetMetaDataImplTest.java

@@ -77,6 +77,18 @@ public void testGetColumnTypeIntegers() throws Exception {
         }
     }
 
+    @Test
+    public void testGetColumnTypeMap() throws Exception {
+        try (Connection conn = getJdbcConnection()) {
+            try (Statement stmt = conn.createStatement()) {
+                ResultSet rs = stmt.executeQuery("select map('a', 1) as a");
+                ResultSetMetaData rsmd = rs.getMetaData();
+                assertEquals(rsmd.getColumnType(1), Types.JAVA_OBJECT);
+                assertEquals(rsmd.getColumnClassName(1), Object.class.getName());
+            }
+        }
+    }
+
     @Test(groups = { "integration" })
     public void testGetColumnTypeFloats() throws Exception {
         try (Connection conn = getJdbcConnection()) {