```_FillValue``` and ```missing_value``` attributes get removed when using ```open_dataset```

[Whyborn]

What is your issue?

When opening an NetCDF dataset using open_dataset, the attributes _FillValue and missing_value of the underlying Datasets are removed (unless mask_and_scale = false). It seems counterintuitive to lose information by default, especially information which is necessary to determine what exactly the input data looked like.

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[kmuehlbauer]

@Whyborn The attributes are moved to .encoding attribute of the respective DataArray in case of decoding. Please also follow-up with #6323.

[kmuehlbauer]

@Whyborn Did my above comment shed some light? Please let us know if you need further information.

[kmuehlbauer]

I'll close this for now, please let us know, if you need more information.