I added your test (done 10 times),

executions = 10
test = "np.array([None]*100000, dtype=np.float64)"
t = timeit.timeit(test, setup=code, number=executions)
print formatresults(test, t)

My pull request does it at, 
0.216 [s]

your suggested code does it at,
0.963 [s]

no modifications at all,
2.307 [s]