IntelliJ: html package not created/accessed (setURLHierarchy)

[P5music]

This is happening with an IntelliJ project: I create the html package (under src) so to load an HTML file in a WebView like this
webView.setURLHierarchy("/filename.html");
the HTML file is inside that folder
but the "File not found" error is issued.

IDE: IntelliJ IDEA 2020.1.3 (Community Edition)
Build #IC-201.8538.31, built on July 7, 2020
Runtime version: 11.0.7+10-b765.64 amd64
VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o.
Linux 5.4.0-42-generic
GC: ParNew, ConcurrentMarkSweep
Memory: 949M
Cores: 4
Non-Bundled Plugins: com.codename1.plugin.intellij, org.jetbrains.kotlin
Current Desktop: ubuntu:GNOME