How does one get into do nothing Java?

To get do nothing Java - 
Firstly, how is this:
if (cond1) {
    ...
} else if (cond2) {
    NULL;
} else {
    ...
}
Better than:
if (cond1) {
    ...
} else if (cond2) {
} else {
    ...
}
The NULL;-statement doesn't tell anything, or does it?
Secondly, as others pointed out, you don't have to have that empty block, unless you need to say something about the condition or possibly leave space to handle it.
So this makes perfect sense:
if (cond1) {
    ...
} else if (cond2) {
    //cond2 is not handled, because 2 is the smallest prime number
} else {
    ...
}
Or this:
if (cond1) {
    ...
} else if (cond2) {
    //TODO: investigate whether/how this condition needs to be handled
} else {
    ...
}

However an undocumented empty consequence serves no purpose, whether you write NULL; in there or not. Lastly, if you feel like you are having too many conditions, then you should investigate how behavioural patterns and polymorphism in general could help you clean up your code.