Automatic script does not work on Raspbian (Buster)

$ sudo bash -c "$(wget -O - https://apt.llvm.org/llvm.sh)"
--2024-10-18 10:42:38--  https://apt.llvm.org/llvm.sh
Resolving apt.llvm.org (apt.llvm.org)... 199.232.198.49, 199.232.194.49, 2a04:4e42:4c::561, ...
Connecting to apt.llvm.org (apt.llvm.org)|199.232.198.49|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 5811 (5.7K) [application/octet-stream]
Saving to: ‘STDOUT’

-                       100%[============================>]   5.67K  --.-KB/s    in 0.003s

2024-10-18 10:42:38 (1.78 MB/s) - written to stdout [5811/5811]

+ CURRENT_LLVM_STABLE=18
+ BASE_URL=http://apt.llvm.org
+ needed_binaries=(lsb_release wget add-apt-repository gpg)
+ missing_binaries=()
+ for binary in "${needed_binaries[@]}"
+ which lsb_release
+ for binary in "${needed_binaries[@]}"
+ which wget
+ for binary in "${needed_binaries[@]}"
+ which add-apt-repository
+ for binary in "${needed_binaries[@]}"
+ which gpg
+ [[ 0 -gt 0 ]]
+ LLVM_VERSION=18
+ ALL=0
++ lsb_release -is
+ DISTRO=Raspbian
++ lsb_release -sr
+ VERSION=10
+ UBUNTU_CODENAME=
+ CODENAME_FROM_ARGUMENTS=
+ source /etc/os-release
++ PRETTY_NAME='Raspbian GNU/Linux 10 (buster)'
++ NAME='Raspbian GNU/Linux'
++ VERSION_ID=10
++ VERSION='10 (buster)'
++ VERSION_CODENAME=buster
++ ID=raspbian
++ ID_LIKE=debian
++ HOME_URL=http://www.raspbian.org/
++ SUPPORT_URL=http://www.raspbian.org/RaspbianForums
++ BUG_REPORT_URL=http://www.raspbian.org/RaspbianBugs
+ DISTRO=raspbian
+ case ${DISTRO} in
+ [[ -n '' ]]
+ '[' 0 -ge 1 ']'
+ getopts :hm:n: arg
+ [[ 0 -ne 0 ]]
+ declare -A LLVM_VERSION_PATTERNS
+ LLVM_VERSION_PATTERNS[9]=-9
+ LLVM_VERSION_PATTERNS[10]=-10
+ LLVM_VERSION_PATTERNS[11]=-11
+ LLVM_VERSION_PATTERNS[12]=-12
+ LLVM_VERSION_PATTERNS[13]=-13
+ LLVM_VERSION_PATTERNS[14]=-14
+ LLVM_VERSION_PATTERNS[15]=-15
+ LLVM_VERSION_PATTERNS[16]=-16
+ LLVM_VERSION_PATTERNS[17]=-17
+ LLVM_VERSION_PATTERNS[18]=-18
+ LLVM_VERSION_PATTERNS[19]=-19
+ LLVM_VERSION_PATTERNS[20]=
+ '[' '!' _ ']'
+ LLVM_VERSION_STRING=-18
bash: line 140: CODENAME: unbound variable

Reproduce the command on Raspbian GNU/Linux 10 (buster) and inspect the downloaded llvm.sh around line 140, where CODENAME is reported as unbound. Compare the script's distro and release detection for Raspbian with the failing trace. Done means the automatic installation command completes successfully on Raspbian Buster.