Starts to add null data patterns to methods

[sckott]

fix #95

let me know what you think @zachary-foster

[codecov-io]

Codecov Report

Merging #107 into master will decrease coverage by 0.12%.
The diff coverage is 76%.

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
- Coverage   76.38%   76.25%   -0.13%     
==========================================
  Files          21       21              
  Lines        2071     2085      +14     
==========================================
+ Hits         1582     1590       +8     
- Misses        489      495       +6

Impacted Files	Coverage Δ
R/taxon_rank.R	100% <100%> (ø)	⬆️
R/taxon_name.R	100% <100%> (ø)	⬆️
R/taxon_id.R	100% <100%> (ø)	⬆️
R/taxon.R	92.3% <100%> (+0.15%)	⬆️
R/hierarchy.R	33.33% <33.33%> (-0.41%)	⬇️
R/taxa.R	92.59% <86.66%> (-7.41%)	⬇️

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[zachary-foster]

LGTM