The bug arises when a module has a concealed package but it doesn't have the ModulePackages class file attribute. Here's a quick example with an exploded module, it also happens with modular JARs.

mkdir -p src/m/p src/m/q
cat > src/m/module-info.java << EOF
module m { exports p; }
EOF
cat > src/m/p/C.java << EOF
package p;
class C { }
EOF
cat > src/m/q/C.java << EOF
package q;
class C { }
EOF
mkdir -p mods/m
javac -d mods/m $(find src -name "*.java")
java -p mods --list-modules m
jlink --module-path $JAVA_HOME/jmods:mods --add-modules m --output myimage