--strictNullChecks doesn't recongnize error that throw from nested method

[xujihui1985]

TypeScript Version: 1.8.0 / nightly (2.0.0-dev.201xxxxx)
2.0.0
Code

// A *self-contained* demonstration of the problem follows...
with --strictNullChecks options, 
always complain `function lack ending return`, I throw the error in another method instead of throw it right awary. doesn't recongnize method that throw error in another method.

Expected behavior:
should compile success
Actual behavior:
can not be compiled

[RyanCavanaugh]

Same root cause (and fix) as #9655

[xujihui1985]

@RyanCavanaugh thanks for reply