24 hour format setting in Android

When i was developing a date time picker component for our customer, there was a request from them.

When user selects time, show 24 hour format with user setting. If user uses 12 hour format in his/her phone settings, show AM/PM selection, otherwise don't show this selection.

In Android, to get 24 hour setting from user settings, i have used following code lines to get 24 hour format of user.

Settings.System.getString(context.getContentResolver(), Settings.System.TIME_12_24);

When i was testing application on different phones, i received this value as a null on some phones.When i was researching Android SDK, there was an another method to get 24 hour format from setting.

android.text.format.DateFormat.is24HourFormat(context)

No error and i got 24 hour format setting on all test phones. What is happening? When i check DateFormat.java file from source code of Android, there is the tricky :

    
public static boolean is24HourFormat(Context context) {
    String value = Settings.System.getString(context.getContentResolver(), 
                                             Settings.System.TIME_12_24);
    if (value == null) {
        ...
        ...

is24HourFormat function also checks Settings.System.TIME_12_24 setting and if it is null, get setting from another way. So, keep using DateFormat.is24HourFormat(context) to get 24 hour format in application.