-buildDrafts option -> "range can't iterate over presets"

[jmead23]

hugo version 0.71 (also .70)
theme version: .90

When I add option -buildDrafts I get an error ending "range can't iterate over presets". If I go back to version .40, the error goes away.

Here's the entire commandline error:

Error: Error building site: failed to render pages: render of "page" failed: exe
cute of template failed: template: _default/single.html:4:4: executing "_default
/single.html" at <partial "head.html" .>: error calling partial: execute of temp
late failed: template: _internal/schema.html:22:82: executing "_internal/schema.
html" at <.Params.tags>: range can't iterate over presets

I'm still just learning Hugo, so my site isn't very big, nor interesting.