[Bug] Merging empty lists halts subsequent environment variable processing

[twsearle]

Current behavior (describe the bug)

Subsequent to merging a file containing an empty list, no further env variables are processed.

To Reproduce

Make the following files:

./empty_include.yaml

[]

./test.yaml

- filter: ${VARIABLE_1}
- INCLUDE: empty_include.yaml
  MERGE: true
- filter: ${VARIABLE_1}

Process with VARIABLE_1=test yp-data test.yaml -o test_out.yaml

Output is:

./test_out.yaml

- filter: test
- filter: ${VARIABLE_1}

Expected behavior

Output ought to be:

- filter: test
- filter: test

[twsearle]

PS47 requirement is for this file: https://github.com/MetOffice/jjaux/blob/47.0.2-20240608T0000Z/operational/ocean/global-ocean/sla_doNotAssimilate_InOneFile.yaml

[matthewrmshin]

Thanks. I've repeated the problem in a new test. I'll try to find a fix.

[twsearle]

Re-opened, as the solution to this issue caused another, similar issue.