TS Semantic Error - src/common/motion/position.ts(975,42): error TS2345

[jpoon]

Just tried to build master locally. We're getting a semantic TS error that is being ignored (build still succeeds). Same repro on Travis.

[10:56:07] Finished 'tslint' after 2.77 s
src/common/motion/position.ts(975,42): error TS2345: Argument of type 'number | ((start?: number | undefined, end?: number | undefined) => number[]) | ((...items: numbe...' is not assignable to parameter of type 'number'.
  Type '(start?: number | undefined, end?: number | undefined) => number[]' is not assignable to type 'number'.
TypeScript: 1 semantic error
TypeScript: emit succeeded (with errors)