Sonar - Avoid throwing NullPointerException

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6229 0c6e7542-c601-0410-84e7-c038aed88b3b
Sonar - Don't create instances of already existing BigInteger ZERO

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6230 0c6e7542-c601-0410-84e7-c038aed88b3b
Sonar - Avoid instantiating Integer objects. Call Integer.valueOf() instead (more memory-friendly)

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6231 0c6e7542-c601-0410-84e7-c038aed88b3b
Sonar - Avoid unused local variables

git-svn-id: http://josm.openstreetmap.de/svn/trunk@6232 0c6e7542-c601-0410-84e7-c038aed88b3b