override sum for cached AbstractFill

[dlfivefifty]

No description provided.

[codecov]

Codecov Report

Merging #149 (40c95ad) into master (d54f863) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #149      +/-   ##
==========================================
+ Coverage   88.46%   88.47%   +0.01%     
==========================================
  Files          12       12              
  Lines        1647     1649       +2     
==========================================
+ Hits         1457     1459       +2     
  Misses        190      190              

Impacted Files	Coverage Δ
src/cache.jl	86.51% <ø> (+0.15%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d54f863...40c95ad. Read the comment docs.