}
    }

    @Override
    public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
      synchronized (mutex) {
        return navigableMap(delegate().headMap(toKey, inclusive), mutex);
      }
    }

    @Override
    public SortedMap<K, V> headMap(K toKey) {
      return headMap(toKey, false);
    }

    @Override
    @CheckForNull

    }

    @Override
    public NavigableMap<K, Collection<V>> headMap(@ParametricNullness K toKey) {
      return headMap(toKey, false);
    }

    @Override
    public NavigableMap<K, Collection<V>> headMap(@ParametricNullness K toKey, boolean inclusive) {
      return new NavigableAsMap(sortedMap().headMap(toKey, inclusive));
    }

    @Override

    }

    @Override
    public SortedMap<K, V> headMap(@ParametricNullness K toKey) {
      return headMap(toKey, false);
    }

    @Override
    public NavigableMap<K, V> headMap(@ParametricNullness K toKey, boolean inclusive) {
      return Maps.unmodifiableNavigableMap(delegate.headMap(toKey, inclusive));
    }

    @Override

    }

    @Override
    public SortedMap<K, V> headMap(@ParametricNullness K toKey) {
      return headMap(toKey, false);
    }

    @Override
    public NavigableMap<K, V> headMap(@ParametricNullness K toKey, boolean inclusive) {
      return Maps.unmodifiableNavigableMap(delegate.headMap(toKey, inclusive));
    }

    @Override

    /**
     * A key corresponding to the spec that is an immutable snapshot of the spec properties
     * suitable for usage in collections.
     */
    interface Key {}

    Key toKey();

    /**
     * A spec is considered configured when at least {@link #getLanguageVersion() language version} is set.
     * <p>
     * A spec that is not configured always directly matches the toolchain of the current JVM.

    public DefaultToolchainSpec() {
        getVendor().convention(getConventionVendor());
        getImplementation().convention(getConventionImplementation());
    }
    @Override
    public JavaToolchainSpecInternal.Key toKey() {
        return new Key(getLanguageVersion().getOrNull(), getVendor().getOrNull(), getImplementation().getOrNull());
    }

    @Override
    public boolean isConfigured() {

        return objectFactory.newInstance(SpecificInstallationToolchainSpec.class, JavaExecutableUtils.resolveJavaHomeOfExecutable(executable));
    }

    @Override
    public Key toKey() {
        return new Key(javaHome);
    }

    @Override
    public boolean isConfigured() {
        return true;
    }

    @Override
    public boolean isValid() {
        return true;
    }

							fromKey := from.Config().ClusterLocalFQDN()
							toKey := to.Config().ClusterLocalFQDN()
							if testTopology[fromKey] == nil {
								testTopology[fromKey] = map[string]int{}
							}
							testTopology[fromKey][toKey]++
						})
				},
				expect: map[string]map[string]int{
					"a.echo1.svc.cluster.local": {

        // We can't use the key of the fallback toolchain spec, because it is a spec that can match configured requests as well
        JavaToolchainSpecInternal.Key actualKey = useFallback ? FALLBACK_TOOLCHAIN_KEY : requestedSpec.toKey();

        Object resolutionResult = matchingToolchains.computeIfAbsent(actualKey, key -> {
            try {
                return query(actualSpec, useFallback);
            } catch (Exception e) {

					res[fromKey] = map[Reference]*Grants{}
				}
				if _, f := res[fromKey][toKey]; !f {
					res[fromKey][toKey] = &Grants{
						AllowedNames: sets.New[string](),
					}
				}
				if to.Name != nil {
					res[fromKey][toKey].AllowedNames.Insert(string(*to.Name))
				} else {
					res[fromKey][toKey].AllowAll = true
				}
			}
		}
	}
	return res
}