[bug] Empty source conandata.yml file gives error with scm_to_conandata during recipe export

[SeanSnyders]

Environment Details (include every applicable attribute)

• Operating System+version: macOS OSX 10.15.6 (Darwin machine_name 19.6.0 Darwin Kernel Version 19.6.0: Thu Jun 18 20:49:00 PDT 2020; root:xnu-6153.141.1~1/RELEASE_X86_64 x86_64)
• Compiler+version: n/a
• Conan version: 1.30.2
• Python version: 3.9.1

Steps to reproduce (Include if Applicable)

The goal was to have a recipe without (currently) any other data/settings in the conandata.yml, but use the SCM feature.

1. Simple conan recipe conanfile.py but using SCM feature and value of entry url, and revision both set to auto.
2. Add empty conandata.yml next to conanfile.py
3. update ~/.conan/conan.conf to set scm_to_conandata = True
4. export recipe conan export . user/testing --ignore-dirty

Gives error:

5. Update empty conandata.yml to contain a dummy entry, e.g. dummy: on first line
6. re-run export conan export . user/testing --ignore-dirty

Succeeds with SCM data written to the local conan cache export:

Logs (Executed commands with output) (Include/Attach if Applicable)

See above.

[SeanSnyders]

As a side note, if there are no conandata.yml then the export works fine.
Seems to only be an issue if the conandata.yml is empty.

[memsharded]

Thanks for the detailed report @SeanSnyders

Indeed a bug, already submitted #8215, will be in next Conan 1.33