Error when running make

[Calinou]

On Fedora 27 with Python 3.6.3, running make fails with the error below:

mkdir -p build
./bpgen.py
Loading emotes
Processing
Traceback (most recent call last):
  File "./bpgen.py", line 151, in <module>
    main()
  File "./bpgen.py", line 135, in main
    tag_id2name, tag_name2id = bplib.resolve.build_tag_map(all_emotes, context)
  File "/home/hugo/Documents/Git/Rothera/bpm/bplib/resolve.py", line 125, in build_tag_map
    tag_name2id[alias] = tag_name2id[name]
KeyError: '+tempestshadow'
make: *** [Makefile:84: build/bpm-resources.js] Error 1

This was tested on commit 15a554d; this error does not occur on previous commits.