Update CustomTable.java

[wodencafe]

Add null checks to avoid a strange situation with Null Pointer Exceptions.

We triggered this somehow, with code that worked with FilterTable 0.9.9.v7, but broke with 0.9.11.v7.

These null checks protect against the issue.

[ikus060]

I need some instruction to compile it. I'm used to maven, not Ivy. I've try running the following command: java -jar /usr/share/java/ivy.jar Most dependencies are resolved, but popupbutton v 2.4.1 is not.