retain subfield of element that may or may not be an array breaks

[TobiasNx]

"https://raw.githubusercontent.com/metafacture/metafacture-core/master/metafacture-runner/src/main/dist/examples/read/marc21/10.marc21"
| open-http
| as-lines
| decode-marc21
| fix("retain('65???.*.a')")
| encode-formeta(style="multiline")
| print
;

"https://raw.githubusercontent.com/metafacture/metafacture-core/master/metafacture-runner/src/main/dist/examples/read/marc21/10.marc21"
| open-http
| as-lines
| decode-marc21
| fix("retain('65???.a')")
| encode-formeta(style="multiline")
| print
;

Both break