Building the vignette fails at pk_anatomical_detail()

[hlapp]

Here's the corresponding output:

* creating vignettes ... ERROR
Warning in .nextMethod(obj = obj, from = from) :
  NAs introduced by coercion
....This might take a while....
https://scholar.google.com/scholar?q=The+Phylogeny+of+Ictalurid+Catfishes%3A+A+Synthesis+of+Recent+Work&btnG=&hl=en&as_sdt=0%2C42
Parse NeXML....
Map symbols to labels...
Quitting from lines 106-107 (rphenoscape.Rmd) 
Error: processing vignette 'rphenoscape.Rmd' failed with diagnostics:
Each variable must be a 1d atomic vector or list.
Problem variables: relationships.
Execution halted
Error: Command failed (1)
Execution halted

The respective code chunk is the following:

pk_anatomical_detail("basihyal bone")

I suspect that's related to the test failure reported in #6.

[hlapp]

The underlying issue for this is, I think, the same as for #6. See phenoscape/phenoscape-kb-services#43.