ADDITIONAL SYSTEM INFORMATION :
openjdk full version "14+36-1461"

A DESCRIPTION OF THE PROBLEM :
The behavior of Xdoclint's "missing" group doesn't work as expected for javadoc (note that it does for javac)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
* create 2 directories, 1 named "docs", 1 named "foo"
* in "foo", create a file Doc.java as provided below
* open a terminal in "docs" and run the following 2 commands:
** javadoc -private -Xdoclint:all ../foo/Doc.java
** javac -Xdoclint:all ../foo/Doc.java

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Both commands give equivalent results and report 3 warnings, namely:
..\foo\Doc.java:4: warning: documentation comment not expected here
package foo;
^
..\foo\Doc.java:6: warning: no comment
public class Doc {
       ^
..\foo\Doc.java:8: warning: no comment
    public void bar() {
                ^
3 warnings
ACTUAL -
The javadoc command doesn't report any warnings, whereas the javac command reports the expected result.

---------- BEGIN SOURCE ----------
/**
 * Something unexpected.
 */
package foo;

public class Doc {

    public void bar() {

    }

}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use javac instead of javadoc