[fix](schema scan) Fix NPE for schema scan (#59389)

Introduced by #55334

java.lang.reflect.InvocationTargetException: null
at jdk.internal.reflect.GeneratedMethodAccessor90.invoke(Unknown Source)
~[?:?]
at
jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
~[?:?]
	at java.lang.reflect.Method.invoke(Method.java:569) ~[?:?]
at org.apache.doris.service.FeServer.lambda$start$0(FeServer.java:60)
~[doris-fe.jar:1.2-SNAPSHOT]
	at jdk.proxy2.$Proxy47.describeTables(Unknown Source) ~[?:?]
at
org.apache.doris.thrift.FrontendService$Processor$describeTables.getResult(FrontendService.java:4122)
~[fe-common-1.2-SNAPSHOT.jar:1.2-SNAPSHOT]
at
org.apache.doris.thrift.FrontendService$Processor$describeTables.getResult(FrontendService.java:4102)
~[fe-common-1.2-SNAPSHOT.jar:1.2-SNAPSHOT]
at org.apache.thrift.ProcessFunction.process(ProcessFunction.java:38)
~[libthrift-0.16.0.jar:0.16.0]
at org.apache.thrift.TBaseProcessor.process(TBaseProcessor.java:38)
~[libthrift-0.16.0.jar:0.16.0]
at
org.apache.thrift.server.TThreadPoolServer$WorkerProcess.run(TThreadPoolServer.java:250)
~[libthrift-0.16.0.jar:0.16.0]
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
~[?:?]
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
~[?:?]
	at java.lang.Thread.run(Thread.java:840) ~[?:?]
Caused by: java.lang.NullPointerException: Cannot invoke
"org.apache.doris.catalog.TableIf.isTemporary()" because "table" is null
at
org.apache.doris.service.FrontendServiceImpl.describeTables(FrontendServiceImpl.java:971)
~[doris-fe.jar:1.2-SNAPSHOT]
	... 13 more
2025-12-25 20:00:07,417 ERROR (thrift-server-pool-5530|154)
[ProcessFunction.process():47] Internal error processing describeTables
java.lang.reflect.UndeclaredThrowableException: null
	at jdk.proxy2.$Proxy47.describeTables(Unknown Source) ~[?:?]
at
org.apache.doris.thrift.FrontendService$Processor$describeTables.getResult(FrontendService.java:4122)
~[fe-common-1.2-SNAPSHOT.jar:1.2-SNAPSHOT]
at
org.apache.doris.thrift.FrontendService$Processor$describeTables.getResult(FrontendService.java:4102)
~[fe-common-1.2-SNAPSHOT.jar:1.2-SNAPSHOT]
at org.apache.thrift.ProcessFunction.process(ProcessFunction.java:38)
~[libthrift-0.16.0.jar:0.16.0]
at org.apache.thrift.TBaseProcessor.process(TBaseProcessor.java:38)
~[libthrift-0.16.0.jar:0.16.0]
at
org.apache.thrift.server.TThreadPoolServer$WorkerProcess.run(TThreadPoolServer.java:250)
~[libthrift-0.16.0.jar:0.16.0]
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
~[?:?]
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
~[?:?]
	at java.lang.Thread.run(Thread.java:840) ~[?:?]
Caused by: java.lang.reflect.InvocationTargetException
at jdk.internal.reflect.GeneratedMethodAccessor90.invoke(Unknown Source)
~[?:?]
at
jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
~[?:?]
	at java.lang.reflect.Method.invoke(Method.java:569) ~[?:?]
at org.apache.doris.service.FeServer.lambda$start$0(FeServer.java:60)
~[doris-fe.jar:1.2-SNAPSHOT]
	... 9 more
Caused by: java.lang.NullPointerException: Cannot invoke
"org.apache.doris.catalog.TableIf.isTemporary()" because "table" is null
at
org.apache.doris.service.FrontendServiceImpl.describeTables(FrontendServiceImpl.java:971)
~[doris-fe.jar:1.2-SNAPSHOT]
at jdk.internal.reflect.GeneratedMethodAccessor90.invoke(Unknown Source)
~[?:?]
at
jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
~[?:?]
	at java.lang.reflect.Method.invoke(Method.java:569) ~[?:?]
at org.apache.doris.service.FeServer.lambda$start$0(FeServer.java:60)
~[doris-fe.jar:1.2-SNAPSHOT]
	... 9 more

Author: Gabriel39

fe/fe-core/src/main/java/org/apache/doris/service/FrontendServiceImpl.java

@@ -895,13 +895,13 @@ public TDescribeTablesResult describeTables(TDescribeTablesParams params) throws
         if (db != null) {
             for (String tableName : tables) {
                 TableIf table = db.getTableNullableIfException(tableName);
-                if (table.isTemporary()) {
-                    // because we return all table names to be,
-                    // so when we skip temporary table, we should add a offset here
-                    tablesOffset.add(columns.size());
-                    continue;
-                }
                 if (table != null) {
+                    if (table.isTemporary()) {
+                        // because we return all table names to be,
+                        // so when we skip temporary table, we should add a offset here
+                        tablesOffset.add(columns.size());
+                        continue;
+                    }
                     table.readLock();
                     try {
                         List<Column> baseSchema = table.getBaseSchemaOrEmpty();