puppet parser validate version 6.6.0 does not accept STDIN properly

Puppet Version: 6.6.0 and 6.5.0
Puppet Server Version: N/A
OS Name/Version: Ubuntu 19.04 using bionic packages 6.6.0-1bionic

Passing code over stdin to puppet parser fails with 'Error: undefined method `message' for nil:NilClass'. I was able to reproduce with 6.5.0 and 6.6.0, but not with 6.4.2

Desired Behavior:

Validation of code using filename or stdin should be identical

Actual Behavior:

> touch foo.pp
> puppet parser validate foo.pp
> cat foo.pp | puppet parser validate
Error: undefined method `message' for nil:NilClass
Error: Try 'puppet help parser validate' for usage

I noticed this because emacs flycheck uses stdin to do syntax checking.

Note that the documentation (man puppet parser) states that this is a valid way to submit output:

EXAMPLES

Validate from STDIN:

$ cat init.pp | puppet parser validate