Fix an NPE when adding creators
Fix an NPE when adding creators

Do not initialize the array of creators to "null" but to an empty array to
avoid an NPE when adding creators later. It is in line with other calls
to "new SPDXCreatorInformation()" to pass "new String[] {  }" instead of
"null".

Signed-off-by: Sebastian Schuberth <77397652b38ec60b50e56236b813774ce842bcdf@gmail.com>

spdx/tools,spdx/tools