#vulnerable code 
                                @Test
    public void shouldMigrate() {
        HashMap<String, Object> input = new HashMap<>(ImmutableMap.of("main", new HashMap<>(ImmutableMap.of("configVersion", 1))));
        HashMap<String, Object> afterMigration = new HashMap<>(ImmutableMap.of("main", new HashMap<>(ImmutableMap.of("configVersion", 2))));

        when(configMigrationStepMock.forVersion()).thenReturn(1);
        when(configMigrationStepMock.migrate(any())).thenReturn(afterMigration);
        testee.steps = Arrays.asList(configMigrationStepMock);
        testee.expectedConfigVersion = 2;

        Map<String, Object> result = testee.migrate(input);

        verify(configMigrationStepMock).migrate(input);
        assertThat((int) ((Map<String, Object>) result.get("main")).get("configVersion")).isEqualTo(2);
    } 
                            #location 14 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void shouldMigrate() {
        BaseConfig input = new BaseConfig();
        input.getMain().setConfigVersion(1);
        BaseConfig afterMigration = new BaseConfig();
        afterMigration.getMain().setConfigVersion(2);

        when(configMigrationStepMock.forVersion()).thenReturn(1);
        when(configMigrationStepMock.migrate(any())).thenReturn(afterMigration);
        testee.steps = Arrays.asList(configMigrationStepMock);
        testee.expectedConfigVersion = 2;

        BaseConfig result = testee.migrate(input);

        verify(configMigrationStepMock).migrate(input);
        assertThat(result.getMain().getConfigVersion()).isEqualTo(2);
    }