Adapt to enabling error level for the StringSplitter bug pattern

Fix the current issues so that the build continues to work.

When replacing String#split(String) with
Splitter.on(String).splitToList(String) one has to take into account
that the former method expects a regular expression while the latter one
expects a separator string.

Bug: Issue 15077
Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: Ied671f0e72c24a5a33ca5d167d1a1ccfcce27e5b