You will be provided with the source code for an SIP app. On phones running Android 5 Lollipop, the app produces the error 'NullPointerException' when attempting to make an SIP call. Your task is to fix this error and modify existing popups/dialogs in the app to use the standard Android style/design. As a result, all popups in the app should display the basic design/style of the corresponding Android version running on the phone, including Android 5 Lollipop.
On completion, you will be required to send the specific files which have been changed in the source.