*         .header("Proxy-Authorization", "secret")
 *         .build();
 *   }
 * }
 * return null; // Didn't find a preemptive auth scheme.
 * ```
 *
 * ## Reactive Authentication
 *
 * Implementations authenticate by returning a follow-up request that includes an authorization
 * header, or they may decline the challenge by returning null. In this case the unauthenticated
 * response will be returned to the caller that triggered it.
 *

                                    propertyName, valueClass == null ? null : valueClass.getName(),
                                    valueClass == null ? null : valueClass.getClassLoader(), convertedValue,
                                    targetClass == null ? null : targetClass.getName(),
                                    targetClass == null ? null : targetClass.getClassLoader() }).initCause(t);
                }

    if (expectedSequenceNumber != ANY_SEQUENCE_NUMBER &&
      (entry == null || entry.sequenceNumber != expectedSequenceNumber)
    ) {
      return null // Snapshot is stale.
    }

    if (entry?.currentEditor != null) {
      return null // Another edit is in progress.
    }

    if (entry != null && entry.lockingSourceCount != 0) {
      return null // We can't write this file because a reader is still reading it.
    }

            this.releases = new LinkedList<>();
        } else {
            this.acquires = null;
            this.releases = null;
        }
    }

    boolean matches(final String shr, final String servc) {
        return this.share.equalsIgnoreCase(shr) && (servc == null || servc.startsWith("??") || this.service.equalsIgnoreCase(servc));
    }

    @Override

                }
            """
        ) {
            assertHasErrors(
                "Method com.example.Source.foo(): From non-null returning to null-unmarked returning breaking change.",
                "Method com.example.Source.baz(): From non-null returning to null-unmarked returning breaking change.",
            )
            assertHasNoWarning()

    }
    // ------------------------------------------------------------------------
    public MetadataGraphVertex addVertex(ArtifactMetadata md) {
        if (md == null) {
            return null;
        }

        checkVertices();

        MetadataGraphVertex v = findVertex(md);
        if (v != null) {
            return v;
        }

        v = new MetadataGraphVertex(md);

        // and we want artifact resolution to only return the system scoped artifact itself.
        //
        if (artifact.getScope() != null && artifact.getScope().equals(Artifact.SCOPE_SYSTEM)) {
            return new ResolutionGroup(null, null, null);
        }

        ResolutionGroup cached = cache.get(
                artifact,
                request.isResolveManagedVersions(),

        // Match by share name or server address, safely handling nulls
        boolean shareMatch = resourceName != null && shareName != null && resourceName.equalsIgnoreCase(shareName);

        String serverAddress = registration.getServerAddress() != null ? registration.getServerAddress().getHostAddress() : null;
        boolean addressMatch = java.util.Objects.equals(resourceName, serverAddress);

    @Test
    @DisplayName("Setters accept null and getters return null")
    void settersAcceptNull() {
        TestSpnegoToken t = new TestSpnegoToken();
        t.setMechanismToken(null);
        t.setMechanismListMIC(null);
        assertNull(t.getMechanismToken(), "mechanismToken should be null after setting null");
        assertNull(t.getMechanismListMIC(), "mechanismListMIC should be null after setting null");
    }

            VersionResult result) {
        Versioning versioning = null;
        try {
            if (metadata != null) {
                try (SyncContext syncContext = syncContextFactory.newInstance(session, true)) {
                    syncContext.acquire(null, Collections.singleton(metadata));

                    if (metadata.getPath() != null && Files.exists(metadata.getPath())) {