GeezerVison

A nullable variable with a non-null default can legally be used in @skip(if:) or @include(if:). Passing explicit null overrides that default and currently causes an uncaught null-unboxing exception:

query ($flag: Boolean = true) {
  good
  parent { child @skip(if: $flag) }
}

With {"flag": null} and a nullable parent, this now returns {"good": ..., "parent": null} plus an error located at $flag, with path ["parent"].

• Resolve conditional directive arguments through ValuesResolver.getArgumentValues(), reusing the existing Boolean! coercion rules.
• Report root collection failures with data: null; nested failures preserve siblings and follow normal non-null propagation. Include the directive name, argument source location, and enclosing field path where applicable.
• Return subscription event errors without terminating the stream, preserving event extensions. Retain the original error during deferred non-null propagation.
• Preserve Boolean defaults/values, skip short-circuiting, and unknown-variable normalization.

Alternative to #4540: avoids an execution-wide AbortExecutionException. Complements #4522, which handles field arguments before invoking data fetchers; conditional directives are evaluated during field collection.

Validation: 57 new Spock cases cover queries, mutations, fragments, aliases, lists, async fetchers, subscriptions, defer, instrumentation, normalization, and all three DataLoader dispatch modes. ./gradlew --no-daemon test testng jacocoTestReport javadoc passes on Java 25 (6,352 cases, no failures). No per-class coverage regressions against test-baseline.json; the baseline is unchanged.