In the Custom Language Plugin tutorial, step 6: PSI Helpers and Utilities, I defined method findProperties, but when I run my plugin, the definition
Collection<VirtualFile> virtualFiles =
always yields an empty Collection (using IDEA 2021.2.3), returned by getContainingFiles in FileBasedIndexEx.
Is that definition correct? Do I need to define something else first? I do have a MyFileType, but no FileTypeIndex.