Infer count() aggregation is not null #11

Job	Run time
build with wasm-pack	2m 14s
cargo check	3m 43s
Check cargo fmt	43s
cargo test (macos)	8m 49s
cargo test (macos-aarch64)	9m 40s
Verify Vendored Code	52s
Verify MSRV (Min Supported Rust Version)	6m 41s
cargo test (win64)	32m 9s
cargo test (amd64)	9m 22s
cargo test datafusion-cli (amd64)	3m 52s
cargo doc	3m 37s
cargo test doc (amd64)	12m 58s
cargo examples (amd64)	2m 40s
Run sqllogictest with Postgres runner	3m 6s
cargo test pyarrow (amd64)	2m 45s
verify benchmark results (amd64)	10m 21s
check Cargo.toml formatting	2m 46s
clippy	3m 55s
check configs.md is up-to-date	2m 42s
cargo test hash collisions (amd64)	8m 49s
	2h 11m 44s

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