Changing the javadoc link to the JDK docs to be https causes OpenJDK11 to fail

[Capstan]

This is true on all the java-json-tools repositories. I'll put in an exact error message in a bit.

[Capstan]

The error is javadoc: error - The code being documented uses modules but the packages defined in https://docs.oracle.com/javase/7/docs/api/ are in the unnamed module.

This doesn't repro on my dev box, so it's a PITA. It also gives the tantalizing Javadoc generation failed. Generated Javadoc options file (useful for troubleshooting): '/home/travis/build/java-json-tools/btf/build/tmp/javadoc/javadoc.options' but of course I don't have access to that file.

[Capstan]

Instrumenting .travis.yml with

after_failure:
  - if [ -f /home/travis/build/java-json-tools/btf/build/tmp/javadoc/javadoc.options ]; then echo javadoc.options:; cat /home/travis/build/java-json-tools/btf/build/tmp/javadoc/javadoc.options; fi

allowed me to get the javadoc.options file contents:

-classpath '/home/travis/build/java-json-tools/btf/build/classes/java/main:/home/travis/build/java-json-tools/btf/build/resources/main:/home/travis/.gradle/caches/modules-2/files-2.1/com.google.code.findbugs/jsr305/2.0.1/516c03b21d50a644d538de0f0369c620989cd8f0/jsr305-2.0.1.jar'
-d '/home/travis/build/java-json-tools/btf/build/docs/javadoc'
-doctitle 'btf 1.3-SNAPSHOT API'
-link 'https://docs.oracle.com/javase/7/docs/api/'
-link 'https://www.javadoc.io/doc/com.google.code.findbugs/jsr305/3.0.1/'
-quiet 
-windowtitle 'btf 1.3-SNAPSHOT API'
'/home/travis/build/java-json-tools/btf/src/main/java/com/github/fge/Thawed.java'
'/home/travis/build/java-json-tools/btf/src/main/java/com/github/fge/Frozen.java'
'/home/travis/build/java-json-tools/btf/src/main/java/com/github/fge/Builder.java'

Now I just have to figure how to pass the --release flag via gradle.

[Capstan]

javadoc.options.addStringOption("-release", "7"); seems to work, though it's weird to have to prefix it with a '-'. Now I need to apply it only for OpenJDK9 or up.

[Capstan]

Found gradle/gradle/issues/5891 which has a workaround that selects the JDK version.