fix(query): fix array_agg failed if the argument is NULL

[b41sh]

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Summary

1. fix array_agg(NULL) bug
2. add some test for array_agg function

root@0.0.0.0:48000/default> select array_agg(null) from numbers(5);
error: APIError: QueryFailed: [4000]invalid data (Collections of zero-sized types are not allowed due to deny-of-service concerns on deserialization.)

• fixes: #[Link the issue here]

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

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This change is