Correct use of map

[Dfr]

Here is few code eaxamples, i don't know why it is doesn't work 
as expected.

Here i want to transform string into list of tuples split by 
character:

auto nameparts = splitter("go.home", '.').map!(v => 
tuple(v,0)).array;

This gives me not very useful message about assert and stuff:
core.exception.AssertError at std.algorithm(1942): Assertion failure