Rename SERVER_IP to ARDUINO_TESTSERVER_IP or something similar. The PMD Website is currently unavailable [1], but you could try one of these lines to avoid the PMD Warning. First works for Checkstyle and the second for Lint:
// PMD DISABLE AvoidUsingHardCodedIP FOR 1 LINES
@SurpressWarnings("AvoidUsingHardCodedIP")

[1] http://pmd.sourceforge.net/pmd-4.2.5/suppressing.html