[Fix](schema change) Fix NPE when rename column on table which has se…

…quence type column (apache#46906)

### What problem does this PR solve?
Problem Summary:
```mysql
CREATE TABLE `tbl` (
  `c` tinyint NULL,
) ENGINE=OLAP
UNIQUE KEY(`c`)
DISTRIBUTED BY HASH(`c`) BUCKETS 10
PROPERTIES (
  "function_column.sequence_type" = "bigint"
);

mysql> alter table tbl rename column c c_bk;                                                         
ERROR 1105 (HY000): errCode = 2, detailMessage = Cannot invoke "String.equalsIgnoreCase(String)" because the return value of "org.apache.doris.catalog.OlapTable.getSequenceMapCol()" is null
```

fe/fe-core/src/main/java/org/apache/doris/catalog/Env.java

@@ -5225,7 +5225,8 @@ private void renameColumn(Database db, OlapTable table, String colName,
         }
 
         // 5. modify sequence map col
-        if (table.hasSequenceCol() && table.getSequenceMapCol().equalsIgnoreCase(colName)) {
+        if (table.hasSequenceCol() && table.getSequenceMapCol() != null
+                && table.getSequenceMapCol().equalsIgnoreCase(colName)) {
             table.setSequenceMapCol(newColName);
         }
 

regression-test/data/unique_with_mow_p0/test_seq_type_rename_col.out

@@ -0,0 +1,17 @@
+-- This file is automatically generated. You should know what you did if you want to edit this
+-- !sql --
+1	1	1
+2	2	2
+3	3	3
+4	4	4
+5	5	5
+6	6	6
+
+-- !sql --
+1	1	1
+2	2	2
+3	3	3
+4	4	4
+5	5	5
+6	6	6
+

regression-test/suites/unique_with_mow_p0/test_seq_type_rename_col.groovy

@@ -0,0 +1,44 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+suite("test_seq_type_rename_col", "p0") {
+
+    def table1 = "test_seq_type_rename_col"
+    sql "DROP TABLE IF EXISTS ${table1} FORCE;"
+    sql """ CREATE TABLE IF NOT EXISTS ${table1} (
+            `k1` int NOT NULL,
+            `c1` int,
+            `c2` int,
+        )UNIQUE KEY(k1)
+        DISTRIBUTED BY HASH(k1) BUCKETS 1
+        PROPERTIES (
+            "enable_mow_light_delete" = "false",
+            "function_column.sequence_type" = "bigint",
+            "disable_auto_compaction" = "true",
+            "replication_num" = "1"); """
+
+    sql "insert into ${table1}(k1,c1,c2,__DORIS_SEQUENCE_COL__) values(1,1,1,1),(2,2,2,2),(3,3,3,3);"
+    sql "insert into ${table1}(k1,c1,c2,__DORIS_SEQUENCE_COL__) values(4,4,4,4),(5,5,5,5),(6,6,6,6);"
+    sql "sync;"
+    qt_sql "select * from ${table1} order by k1;"
+
+    sql "alter table ${table1} rename column c1 c1_rename;"
+
+
+    qt_sql "select * from ${table1} order by k1;"
+}