AnnDataSet can not be converted to AnnData when the X is empty

[beyondpie]

Hi Kai,

I have several AnnData created directly from fragment files. If I did not add any matrix to AnnData's X, and combine them into AnnDataSet (this step is OK).

1. I find that it always report Errors when I used to_adata function for the merged AnnDataSet object.

thread '' panicked at /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/anndata-0.3.1/src/anndata/dataset.rs:302:81: called Option::unwrap() on a None value note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

2. if I run a.X (a: AnnDataSet), it also reports error:

PanicException: called Option::unwrap() on a None value. (this is the last line of the Error, the whole stacks are about using pretty method to print the results in IPython.)

But AnnData is OK if X is empty. Just nothing is showed in my IPython REPL.

Thanks! Songpeng