Fix bug in error messages for PageRank
Fix bug in error messages for PageRank

shaohua-zhang/incubator-datafu,apache/incubator-datafu,shaohua-zhang/incubator-datafu,shaohua-zhang/incubator-datafu,shaohua-zhang/incubator-datafu,apache/incubator-datafu,shaohua-zhang/incubator-datafu,apache/incubator-datafu,apache/incubator-datafu,apache/incubator-datafu