target_append fails when no initial --target arguments exist

Working on ricochet-build, I have a release project which has no targets, and then adds the outputs of a package output for each target platform like so:

input_files:
 # linux
 - name: linux-i686
   project: package
   target_append:
    - linux
    - linux-i686
 - name: linux-x86_64
   project: package
   target_append:
    - linux
    - linux-x86_64
 # macos
 - name: macos-x86_64
   project: package
   target_append:
    - macos
    - macos-x86_64
 - name: macos-aarch64
   project: package
   target_append:
    - macos
    - macos-aarch64
 # windows
 - name: windows-i686
   project: package
   target_append:
    - windows
    - windows-i686
 - name: windows-x86_64
   project: package
   target_append:
    - windows
    - windows-x86_64

I'm using target_append here so that I can have both signed and unsigned releases built out of ricochet-build. My intention is to build a signed release by:

$ ./rbm/rbm build release --target signed

However if I'm building an unsigned release I was doing (before I changed the various target vars to target_append):

$ ./rbm/rbm build release

Now this fails with:

undef error - Can't use an undefined value as an ARRAY refernece at rbm/lib/RBM.pm line 933

because of this snippet:

            if ($input_file->{target_append}) {
                $input_file->{target} = [ @{$input_file->{target}},
                                          @{ process_template_opt($project,
                                               $input_file->{target_append},
                                               $options) } ];
            }

This is not a blocker to me since I'm going to a additional targets for the release channel (stable vs alpha) and in the short term I can just add a dummy target to initialize the list.