Exit cleanly if nothing to mark

cros_mark_all_as_stable

 #!/bin/bash
 
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Wrapper scripts around cros_mark_as_stable that marks all packages as stable
 # that have CROS_WORKON_COMMIT that is different than the current HEAD commit
 # of the corresponding git repository.
 
@@ skipping 62 matching lines @@
     [ -n "${head_commit}" ]; then
     info\
       "HEAD ${head_commit} != CROS_WORKON_COMMIT ${egit_commit} for ${package}"
     PACKAGE_LIST="${PACKAGE_LIST} ${package}"
     COMMIT_ID_LIST="${COMMIT_ID_LIST} ${head_commit}"
   elif [[ ${head_commit}  = ${egit_commit} ]]; then
     info "Commit id's match for ${package}"
   fi
 done
 
-info "Candidate package list ${PACKAGE_LIST}"
-info "With commit id list ${COMMIT_ID_LIST}"
+if [ -n "${PACKAGE_LIST}" ] ; then
+  info "Candidate package list ${PACKAGE_LIST}"
+  info "With commit id list ${COMMIT_ID_LIST}"
 
-./cros_mark_as_stable --board ${FLAGS_board} -p "${PACKAGE_LIST}" \
-  -i "${COMMIT_ID_LIST}" -t ${FLAGS_tracking_branch} commit  || \
+  ./cros_mark_as_stable --board ${FLAGS_board} -p "${PACKAGE_LIST}" \
+    -i "${COMMIT_ID_LIST}" -t ${FLAGS_tracking_branch} commit  || \
     die "Could not mark all packages as stable"
+else
+  info "No candidate packages to be marked"
+fi