fix: bug importing empty nodes into vizy field via feed-me feed

[yoannisj]

Fiddling around a little bit, I managed to fix #189 with this simple change.

It might not be the best way to address empty nodes from imported feeds, but it prevents the Trying to access array offset on value of type null error and proceeds with importing the rest of the data, leaving the Vizy text empty?

[engram-design]

Thanks for this!