Early exit for empty HashMap (issue #38880)
Addresses issue #38880 by checking if the HashMap is empty before computing the value of the hash.
Before (integer keys)
```
running 4 tests
test empty_once ... bench: 13 ns/iter (+/- 0)
test empty_100 ... bench: 1,367 ns/iter (+/- 35)
test exist_once ... bench: 14 ns/iter (+/- 0)
test exist_100 ... bench: 1,518 ns/iter (+/- 40)
```
After
```
running 4 tests
test empty_once ... bench: 2 ns/iter (+/- 0)
test empty_100 ... bench: 221 ns/iter (+/- 0)
test exist_once ... bench: 15 ns/iter (+/- 0)
test exist_100 ... bench: 1,515 ns/iter (+/- 92)
```
When the HashMap is not empty, the performance remains the same, and when it is empty the performance is significantly improved.
ce89c3de76