Remove Tag.getEmptyValue()

[querz]

Remove Tag.getEmptyValue()

[Querz]

I fixed these so far. ObjectTag#compareTo calls a compareTo method if the values of both ObjectTags implement Comparable. If not, it checks if both values are the same. It returns 1 if the value of this ObjectTag is null but the value of the other isn't and -1 if the value of the other ObjectTag is null but the value of this ObjectTag isn't.

Currently i simply return 0 if none of the above conditions match.

[Querz]

See #27
I also made the Tag() constructor protected so each Tag implementation must specify their own no-args constructor and set their default value. If the only action inside this no-args constructor is a call to Tag(), the value will be null. This might be needed for custom tags (e.g. ObjectTag).

[Marcono1234]

Maybe it would be better to have a validateValue method which by default prevents null and then have ObjectTag override it.

Also there are currently multiple problems with ObjectTag:

• new ObjectTag().setValue(null) throws NPE
• ObjectTag#hashCode throws NPE for null values
• ObjectTag#clone should not catch NPE, instead null check should be done
• ObjectTag#compareTo considers a other null value equal to this, even if this value might not be null