Reusable workflow input with default string is not used when the calling input passed an empty string.

Describe the bug
Reusable workflow input (string) with default is not used when the calling input passed an empty string.
To Reproduce
Steps to reproduce the behavior:

1. reusable workflow

name: 'reusable_workflow'
on:
  workflow_call:
    inputs:
      message:
        description: 'message.'
        type: 'string'
        default: 'default message'
        required: false
jobs:
  print-inputs:
    runs-on: ubuntu-latest
    steps:
      - name: job summary
        run: |
          echo "message: ${{ inputs.message }}" >> $GITHUB_STEP_SUMMARY

2. create a caller workflow that calls 1

name: 'caller'
on:
  workflow_dispatch:
    inputs:
      message:
        description: 'message'
        type: 'string'
        required: false
jobs:
  call-reusable-workflow:
    uses: '.../reusable-workflow.yml@main'
    with:
      message: ${{ inputs.message }}

3. trigger the caller workflow without providing a message input

Expected behavior
should print message: default message

Job Log Output

But print message:

Runner Version and Platform

Version of your runner?

ubuntu-latest

Reproduce the behavior with the reusable workflow and caller workflow shown in the issue, using an omitted or empty message input. Trace how the runner handles workflow_call string defaults, then verify that the job summary prints "message: default message" when the caller provides no message.