async_mode with numpy arrays

[rsluijs]

Windows 7

xlwings 0.14,Office365,Python 2.7

When returning an array in a UDF in combination with the new async_mode, the following error appears:

ValueError: The truth value of an array with more than one element is ambiguous.

@xw.func(async_mode='threading')
@xw.ret(expand='vertical',transpose=True)
def test1(a):
    time.sleep(5)
    b = np.array([a,a])
    return b