#vulnerable code 
                                @Test
    public void testToString() {

        ColumnMapperBuilder columnMapper1 = new ColumnMapperStringBuilder();
        ColumnMapperBuilder columnMapper2 = new ColumnMapperIntegerBuilder();

        Map<String, ColumnMapperBuilder> columnMappers = new HashMap<>();
        columnMappers.put("field1", columnMapper1);
        columnMappers.put("field2", columnMapper2);

        Schema schema = new Schema(columnMappers, null, null);
        assertNotNull(schema.toString());
    } 
                            #location 12 
                            #vulnerability type RESOURCE_LEAK
#fixed code
                                @Test
    public void testToString() {

        ColumnMapperBuilder columnMapper1 = new ColumnMapperStringBuilder();
        ColumnMapperBuilder columnMapper2 = new ColumnMapperIntegerBuilder();

        Map<String, ColumnMapperBuilder> columnMappers = new HashMap<>();
        columnMappers.put("field1", columnMapper1);
        columnMappers.put("field2", columnMapper2);

        Schema schema = new Schema(columnMappers, null, null);
        assertNotNull(schema.toString());
        schema.close();
    }