Update MysqlConnection.java

修复mysql5.6以下报java.lang.NullPointerException

parse/src/main/java/com/alibaba/otter/canal/parse/inbound/mysql/MysqlConnection.java

@@ -281,7 +281,7 @@ public class MysqlConnection implements ErosaConnection {
         }
 
         List<String> columnValues = rs.getFieldValues();
-        if (columnValues != null && columnValues.size() >= 1 && columnValues.get(0).toUpperCase().equals("CRC32")) {
+        if (columnValues != null && columnValues.size() >= 1 && columnValues.get(0)!=null && columnValues.get(0).toUpperCase().equals("CRC32")) {
             binlogChecksum = LogEvent.BINLOG_CHECKSUM_ALG_CRC32;
         } else {
             binlogChecksum = LogEvent.BINLOG_CHECKSUM_ALG_OFF;