When "set -u", "which" outputs environment: line 1: _declare: unbound

[Craig Andrews]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -O2 -flto=auto -ffat-lto-objects -fexceptions -g 
-grecord-gcc-switches -pipe -Wall -Werror=format-security 
-Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS 
-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong 
-specs=/usr/lib/rpm/redhat/redhat-annobin-cc1  -m64  -mtune=generic 
-fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection
uname output: Linux craigatwork 5.11.11-300.fc34.x86_64 #1 SMP Tue Mar 
30 16:37:11 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-redhat-linux-gnu

Bash Version: 5.1
Patch Level: 0
Release Status: release

Description:
        With "set -u", invoking "which" results in the output of: 
environment: line 1: _declare: unboundvariable
        That should not happen, and does not happen, with prior versions 
of bash.
        I'm using Fedora 34 (beta).

Repeat-By:
        Run this shell script:
        #!/bin/bash
        set -u
        echo "$(which bash)"

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