Added handler for properties with null value when inserting

[ArnyminerZ]

Closes #88

[rfc2822]

Please also add the corresponding test and set then to ready when everything is complete :)

[ArnyminerZ]

@rfc2822 Is this enough?

[rfc2822]

@rfc2822 Is this enough?

The tested method is in AndroidEvent, so the test should be in AndroidEventTest.

I think it should be named testBuildUnknownProperty_NoValue(), directly below testBuildUnknownProperty() and similar to that test.

However instead of adding a working unknown parameter, our test should add the unknown property without value (only the unknown parameter, without the rest of the ICalendar). buildEvent() then will call the insert method (which will call our changed method), so we make sure that it doesn't throw an exception. firstUnknownProperty should then return null.

[rfc2822]

Thanks, very good now. Test fails without the fix and passes with the fix :)