为什么无法加入FragmentManager？

[yhlzxq]

我在文件CrimeActivity.java要把Fragment加入FragmentManager的实例化的fm中(红色部分),但却报错“Caused by: java.lang.NullPointerException”,这个错误指向CrimeFragment.java文件中的mTitleField.addTextChangedListener(new TextWatcher(){ 这句话,说明指针未初始化,它是说哪个指针,如果去掉这句话一切正常,为什么会出现这个错误，该怎么办?
public class CrimeActivity extends FragmentActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_crime);

FragmentManager fm=getSupportFragmentManager();
Fragment fragment=fm.findFragmentById(R.id.fragmentcontainer);

if(fragment==null){
fragment=new CrimeFragment();
fm.beginTransaction().add(R.id.fragmentcontainer, fragment).commit();
}
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.fragmentcontainer, new PlaceholderFragment()).commit();
}
}