Call to a member function isHeaderCell() on bool fails

[kyrustech]

Issue Description

Pasting in copied table data from Confluence fails to save or preview when the table contains header cells.

Generates error:
"Call to a member function isHeaderCell() on bool"
"Failed to handle action: save"

Pasting tables without header cells works great, which is awesome.

Additionally, using View Source in Confluence and then copy/paste from the source page also works fine.