Rollup merge of #68598 - GuillaumeGomez:fix-null-synthetic_implementors, r=ollie27
Rollup merge of #68598 - GuillaumeGomez:fix-null-synthetic_implementors, r=ollie27

Fix null synthetic_implementors error

Fixes #68584.

r? @ollie27

cc @kinnison

graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust