empty string instead of NULL. more debug output

git-svn-id: http://svn.osgeo.org/postgis/branches/2.1@12522 b70326c6-7e19-0410-871a-916f4a2858ee
more debug

git-svn-id: http://svn.osgeo.org/postgis/branches/2.1@12523 b70326c6-7e19-0410-871a-916f4a2858ee