Add nullptr check when forwarding from component to datatype

[jleibs]

What

We already have a similar check in our builders, but when a component forwards to the datatype builder, we need a similar check.

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
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[Wumpf]

latest iteration lgtm!
Unforunate that it makes the forwarding so much longer, but don't have a good idea how to avoid that right now (other than some weird macro).