Github user okram commented on the issue:
https://github.com/apache/tinkerpop/pull/748
A `cap()` step is a `SupplyBarrierStep` and thus, requires an emission -- a
single emission, but an emission nonetheless. The ultimate solution step has to
a `FilterStep` by nature so it can truly return "nothing." However, we are now
getting into particulars that don't need arguing. The concept is what matters.
Now that I get the problem, you simply don't want to have to "reattach" and
send data back if you don't have to, then the solution is, filter everything as
the last step. That is, have `iterate()` append to the bytecode a "filter all."
Easy. How that is done, just needs some fiddlin' around.
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