Description

Problem*

Resolves a private issue sent to me on slack

Summary*

Array map is a fairly old method written before we had std::mem::zeroed. Now that we have zeroed, we can allow mapping empty arrays since we can use zeroed to get the filler U value for the starting elements.

Additional Context

While I was at it I included a small clarification to reduce's docs that it requires a non-empty array

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.