As implemented here the initialization is to None as this is slightly more memory efficient than an empty dict {}. However, this makes working with metadata a little more complex as elements can't be added until it's created which requires an if / then. Adam probably anticipated this - what do you think of initialization to {}?

Codecov Report

Merging #928 (3cdb43c) into master (5f65afd) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

❗ Current head 3cdb43c differs from pull request most recent head fb1c302. Consider uploading reports for the commit fb1c302 to get more accurate results

@@            Coverage Diff             @@
##           master     #928      +/-   ##
==========================================
- Coverage   96.11%   96.05%   -0.06%     
==========================================
  Files          39       39              
  Lines        9130     9162      +32     
  Branches     1017     1107      +90     
==========================================
+ Hits         8775     8801      +26     
- Misses        206      209       +3     
- Partials      149      152       +3     

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Does anyone know what the problem is here? The code is working in my build.

Does anyone know what the problem is here? The code is working in my build.

The glibc error in the Linux builds is effecting another PR and will be addressed. You can ignore the codecov failure. It is over-sensitive sometimes.

Not related to this PR @gumyr (which BTW looks good). I'm trying to debug this (CI) issue in #926.

Merging, thanks for the contribution @gumyr !

All green now with the 18.04 fix and it has been approved, so I'm going to merge.

Looks like @adam-urbanczyk beat me to it. Thanks @gumyr