Using two regex question marks '??' in fix function "replaceAll" unexpectedly assumes arrays

[dr0i]

Example:

https://metafacture.org/playground/?flux=%22https%3A//gist.githubusercontent.com/TobiasNx/6c31eaba9dae36a42ed13205ba03ad36/raw/6423be5a05128021ff05733635e200b9956380e1/degruyter_global_EBA-EBKALL_2025-11-16.mrc.ldr-pos17-I.mrc%22%0A%7C+open-http%0A%7C+as-lines%0A%7C+decode-marc21%28emitLeaderAsWhole%3D%22true%22%29%0A%7C+fix%28transformationFile%29%0A%7C+encode-yaml%0A%7C+print%0A%3B&transformation=replace_all%28%22040%3F%3F.a%22%2C%22medium%22%2C%22__medium__%22%29%0A%0Aretain%28%22040%3F%3F%22%29

replace_all("040??.a","medium","__medium__")

retain("040??")

Results in error:

Caused by: java.lang.IllegalStateException: Expected Array or Hash, got String
    at org.metafacture.metafix.Value$TypeMatcher.lambda$orElseThrow$0 (Value.java:525)

[TobiasNx]

I updated the post by @dr0i and added the example.