ADDITIONAL SYSTEM INFORMATION :
affects JDK10 and JDK11. The package-list is present in JDK9 docs...

A DESCRIPTION OF THE PROBLEM :
According to this https://docs.oracle.com/en/java/javase/11/javadoc/javadoc-command.html, a package-list file should be present at this location https://docs.oracle.com/en/java/javase/11/docs/api/ for javadoc to correctly link to api packages. Since this file does not currently exist, if javadoc is run with -link https://docs.oracle.com/en/java/javase/11/docs/api/, a link that is created (e.g. https://docs.oracle.com/en/java/javase/11/docs/api/java/io/InputStream.html?is-external=true) does not include the full package link (java.base) https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/io/InputStream.html

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
run javadoc -d /tmp Foo.java -link 'https://docs.oracle.com/en/java/javase/11/docs/api/'

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
docs link API objects to package documentation
ACTUAL -
docs do not link to package documentation