Is it an elliptical sentence?

Is something omitted in "…is confident will pass." or applied other grammar rule?

It looks like "Adjective" + "Modal Verb + Verb(Simple Future Tense)", which seems strange to me.

Mexico’s lower house has approved a bill that would legalise the
recreational use of cannabis.

It will now go to the Senate for a final vote, which President Andrés
Manuel López Obrador’s party is confident will pass.

Also, is it common for expressing in writing and speaking?

Thank you very much!