Can't create users using useradd provider when specifying uid since 6.8.0

Puppet Version: 6.8.0
Puppet Server Version: 6.4.0
OS Name/Version: Ubuntu 18.04

Creating a user specifying the UID (uses useradd provider automatically):

user { 'test':   ...   uid => 123,}

Desired Behavior:

User is created with uid 123.

Actual Behavior:

Error: Could not create user test1: Execution of '[redacted]' returned 1: Error: Could not execute posix command: no implicit conversion of Integer into String

Debugging showed the command as:

["/usr/sbin/useradd", "-c", "Test1", "-g", "users", "-d", "/home/test1", "-p", "removed", "-s", "/bin/tcsh", "-u", 123, "-m", "test1"]

So I'm assuming the 123 argument there should be quoted.

Suspect this is to do with this change, but can't see why:

https://github.com/puppetlabs/puppet/commit/70d20329012fc986c3d130f5769cc644f248c1b0#diff-f5b9cc80dd02278d845d220721ac0217