fix cassandra code checkstyle

hugegraph-cassandra/src/main/java/com/baidu/hugegraph/backend/store/cassandra/CassandraSessionPool.java

@@ -213,7 +213,9 @@ private void tryOpen() {
             assert this.session == null;
             try {
                 this.open();
-            } catch (InvalidQueryException ignored) {}
+            } catch (InvalidQueryException ignored) {
+                // ignore
+            }
         }
 
         @Override

hugegraph-cassandra/src/main/java/com/baidu/hugegraph/backend/store/cassandra/CassandraShard.java

@@ -208,8 +208,8 @@ private Map<TokenRange, Long> getSubSplits(TokenRange tokenRange,
     private Map<TokenRange, Set<Host>> getRangeMap() {
         Metadata metadata = this.session.metadata();
         return metadata.getTokenRanges().stream().collect(Collectors.toMap(
-                p -> p,
-                p -> metadata.getReplicas('"' + this.keyspace + '"', p)));
+            p -> p,
+            p -> metadata.getReplicas('"' + this.keyspace + '"', p)));
     }
 
     private static Map<TokenRange, Long> describeSplits(

hugegraph-cassandra/src/main/java/com/baidu/hugegraph/backend/store/cassandra/CassandraStore.java

@@ -475,12 +475,12 @@ protected boolean existsKeyspace() {
     }
 
     protected boolean existsTable(String table) {
-         KeyspaceMetadata keyspace = this.cluster().getMetadata()
+        KeyspaceMetadata keyspace = this.cluster().getMetadata()
                                          .getKeyspace(this.keyspace);
-         if (keyspace != null && keyspace.getTable(table) != null) {
-             return true;
-         }
-         return false;
+        if (keyspace != null && keyspace.getTable(table) != null) {
+            return true;
+        }
+        return false;
     }
 
     protected void initKeyspace() {

hugegraph-cassandra/src/main/java/com/baidu/hugegraph/backend/store/cassandra/CassandraTable.java

@@ -107,12 +107,12 @@ public Number queryNumber(CassandraSessionPool.Session session,
             statement.setReadTimeoutMillis(timeout * 1000);
             return session.query(statement);
         }, (q, rs) -> {
-            Row row = rs.one();
-            if (row == null) {
-                return IteratorUtils.of(aggregate.defaultValue());
-            }
-            return IteratorUtils.of(row.getLong(0));
-        });
+                Row row = rs.one();
+                if (row == null) {
+                    return IteratorUtils.of(aggregate.defaultValue());
+                }
+                return IteratorUtils.of(row.getLong(0));
+            });
         return aggregate.reduce(results);
     }