Code building fails on Ubuntu

[PavelTurk]

Code building fails on Ubuntu 20.04.3

pavel@pavel-home:~/Temp$ git clone https://github.com/FXMisc/RichTextFX
Cloning into 'RichTextFX'...
remote: Enumerating objects: 14225, done.
remote: Counting objects: 100% (758/758), done.
remote: Compressing objects: 100% (337/337), done.
remote: Total 14225 (delta 289), reused 665 (delta 231), pack-reused 13467
Receiving objects: 100% (14225/14225), 3.45 MiB | 8.11 MiB/s, done.
Resolving deltas: 100% (6066/6066), done.
pavel@pavel-home:~/Temp$ 
pavel@pavel-home:~/Temp/RichTextFX$ git pull origin pull/1232/head
From https://github.com/FXMisc/RichTextFX
 * branch            refs/pull/1232/head -> FETCH_HEAD
Updating b61a9ae..0a8e212
Fast-forward
 richtextfx/src/main/java/org/fxmisc/richtext/model/StyleSpan.java         | 17 ++++++++++++++++-
 richtextfx/src/main/java/org/fxmisc/richtext/model/StyleSpans.java        | 11 ++++++++++-
 richtextfx/src/main/java/org/fxmisc/richtext/model/StyleSpansBuilder.java | 13 ++++++++++++-
 richtextfx/src/test/java/org/fxmisc/richtext/model/ParagraphTest.java     |  3 +++
 4 files changed, 41 insertions(+), 3 deletions(-)
pavel@pavel-home:~/Temp/RichTextFX$ /opt/gradle-7.5.1/bin/gradle -Dorg.gradle.java.home=/opt/jdk-11.0.2 clean build
Starting a Gradle Daemon, 1 incompatible and 1 stopped Daemons could not be reused, use --status for details

> Configure project :richtextfx
Project :richtextfx => no module-info.java found

> Configure project :richtextfx-demos
Project :richtextfx-demos => no module-info.java found

> Task :richtextfx:compileJava
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

> Task :richtextfx:javadoc
javadoc: error - The code being documented uses packages in the unnamed module, but the packages defined in https://openjfx.io/javadoc/11/ are in named modules.
1 error

> Task :richtextfx:javadoc FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':richtextfx:javadoc'.
> Javadoc generation failed. Generated Javadoc options file (useful for troubleshooting): '/home/pavel/Temp/RichTextFX/richtextfx/build/tmp/javadoc/javadoc.options'

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 42s
7 actionable tasks: 5 executed, 2 up-to-date