IssueTracker

Please include a sample project that reproduces your issue.

This should demonstrate the issue:
https://github.com/zackjp/safeargs-default-values-test

Run the unit test:
https://github.com/zackjp/safeargs-default-values-test/blob/master/app/src/test/java/com/zack/safeargsdefaultvaluestest/DefaultValuesInActionsTest.java

Maybe it is the same as the other issue I listed? Different use case but same root cause?

Switching to Kotlin Safe Args fixed the issue, so seems like the same issue, just on the Directions side (vs the other which is on the Args side).

Project: platform/frameworks/support
Branch: androidx-master-dev

commit 2180ea57914af961d4f2bb43802b42ae0d1802e0
Author: Jeremy Woods <jbwoods@google.com>
Date:   Fri Oct 04 16:02:03 2019

    Generate default values for Directions safe_args in Java
   
    Currently the safe args generation for java code does not contain
    default Direction args values. The default directions arg values are
    provided by the Kotlin safe args generation and we should be as
    uniform as possible across both languages.
   
    Test: ./gradlew --rerun-tasks navigation:navigation-safe-args-gradle-plugin:test
    Change-Id: I07b67d9c86dafff608df49a609796a71a9b3315a
    navigation:navigation-safe-args-generator:test
    BUG: 141099045

M       navigation/navigation-safe-args-generator/src/main/kotlin/androidx/navigation/safe/args/generator/java/JavaNavWriter.kt
M       navigation/navigation-safe-args-generator/src/main/kotlin/androidx/navigation/safe/args/generator/java/JavaTypes.kt
M       navigation/navigation-safe-args-generator/src/tests/test-data/expected/java_nav_writer_test/MainFragmentArgs.java
M       navigation/navigation-safe-args-generator/src/tests/test-data/expected/java_nav_writer_test/MainFragmentDirections.java
M       navigation/navigation-safe-args-generator/src/tests/test-data/expected/java_nav_writer_test/Next.java
M       navigation/navigation-safe-args-generator/src/tests/test-data/expected/java_nav_writer_test/SanitizedMainFragmentDirections.java
M       navigation/navigation-safe-args-generator/src/tests/test-data/expected/nav_generator_test/java/nested_overridden_action/SettingsDirections.java
M       navigation/navigation-safe-args-generator/src/tests/test-data/expected/nav_generator_test/java/nested_same_action/SettingsDirections.java
M       navigation/navigation-safe-args-generator/src/tests/test-data/expected/nav_generator_test/java/nested_same_action/SettingsFragmentDirections.java

https://android-review.googlesource.com/1133433
https://goto.google.com/android-sha1/2180ea57914af961d4f2bb43802b42ae0d1802e0

This has been fixed internally and will be available in the Navigation 2.2.0-beta01 release.

Using '2.2.0-rc02'. Putting null as a default value for a string, returns a string "@null" when getting that parameter from navArgs
<argument
            android:name="deepLinkToken"
            android:defaultValue="@null"
            app:argType="string"
            app:nullable="true" />

And:

val args by navArgs<FragmentArgs>()
args.deepLinkToken // returns "@null"

Re #8 - please file a separate bugs with a project that reproduce your separate issue. If the issue you are mentioning is covered by https://issuetracker.google.com/issues/141613546, feel free to +1.