### What problem does this PR solve?

introduce by #55498

Fix execute copy task fail:
```
Caused by: org.apache.doris.common.AnalysisException: errCode = 2, detailMessage = Cannot invoke "java.util.Optional.isPresent()" because the return value of "org.apache.doris.nereids.trees.plans.co
mmands.info.CopyFromDesc.getFileFilterExpr()" is null
        ... 13 more
Caused by: java.lang.NullPointerException: Cannot invoke "java.util.Optional.isPresent()" because the return value of "org.apache.doris.nereids.trees.plans.commands.info.CopyFromDesc.getFileFilterExpr()" is null
        at org.apache.doris.nereids.trees.plans.commands.info.CopyIntoInfo.doValidate(CopyIntoInfo.java:262) ~[doris-fe.jar:1.2-SNAPSHOT]
        at org.apache.doris.nereids.trees.plans.commands.info.CopyIntoInfo.validate(CopyIntoInfo.java:195) ~[doris-fe.jar:1.2-SNAPSHOT]
        at org.apache.doris.nereids.trees.plans.commands.CopyIntoCommand.run(CopyIntoCommand.java:57) ~[doris-fe.jar:1.2-SNAPSHOT]
        at org.apache.doris.qe.StmtExecutor.executeByNereids(StmtExecutor.java:668) ~[doris-fe.jar:1.2-SNAPSHOT]
        ... 12 more

```

### Release note

None

### Check List (For Author)

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