Accept missing "configuration" key for "chunkKeyEncoding".

[gouttegd]

The DefaultChunkKeyEncoding constructor currently requires a Configuration argument, which means that the Jackson deserializer will fail upon attempting to parse array metadata containing a chunk_key_encoding like this one:

"chunk_key_encoding": {
  "name": "default"
}

Instead, it expects, at a minimum:

"chunk_key_encoding": {
  "name": "default",
  "configuration": {}
}

I believe Zarr-Java is being too strict here. It is true that that the spec for the "Default chunk key encoding" [1] says nothing about the configuration object being optional (it only says that the separator member is optional). But the spec for extension points [2] (and chunk_key_encoding is an extension point) does say that the configuration member MAY be present (and therefore is optional), and in the absence of any overriding statement, I believe configuration should be considered optional also in the context of the "Default chunk key encoding" extension.

There are definitely OME-Zarr files out in the wild with a missing configuration member, for example [3].

This commit relaxes the requirement in the constructor of both the DefaultChunkKeyEncoding and V2ChunkKeyEncoding classes, so that they accept a missing (null) configuration argument and default to using a / and . separator, respectively.

--
[1] https://zarr-specs.readthedocs.io/en/latest/v3/chunk-key-encodings/default/index.html
[2] https://zarr-specs.readthedocs.io/en/latest/v3/core/index.html#extension-definition
[3] https://uk1s3.embassy.ebi.ac.uk/idr/zarr/v0.5/idr0066/ExpD_chicken_embryo_MIP.ome.zarr

[brokkoli71]

Hi @gouttegd,
Thanks for the contribution! This seems like a reasonable relaxation to me