if (method.isAnnotationPresent(Generates.class)) {
        builder.put(method.getReturnType(), method);
      }
    }
    GENERATORS = builder.buildOrThrow();
  }

  private static final ImmutableMap<Class<?>, Method> EMPTY_GENERATORS;

  static {
    ImmutableMap.Builder<Class<?>, Method> builder = ImmutableMap.builder();

          .put("HmacSHA1", SHA1_KEY, Hashing.hmacSha1(SHA1_KEY))
          .put("HmacSHA256", SHA256_KEY, Hashing.hmacSha256(SHA256_KEY))
          .put("HmacSHA512", SHA512_KEY, Hashing.hmacSha512(SHA512_KEY))
          .buildOrThrow();

  public void testNulls() {
    NullPointerTester tester =
        new NullPointerTester().setDefault(String.class, "HmacMD5").setDefault(Key.class, MD5_KEY);

        Type type = mapping.getValue();
        checkArgument(!variable.equalsType(type), "Type variable %s bound to itself", variable);
        builder.put(variable, type);
      }
      return new TypeTable(builder.buildOrThrow());
    }

    final Type resolve(TypeVariable<?> var) {
      TypeTable unguarded = this;
      TypeTable guarded =
          new TypeTable() {
            @Override

        Type type = mapping.getValue();
        checkArgument(!variable.equalsType(type), "Type variable %s bound to itself", variable);
        builder.put(variable, type);
      }
      return new TypeTable(builder.buildOrThrow());
    }

    final Type resolve(TypeVariable<?> var) {
      TypeTable unguarded = this;
      TypeTable guarded =
          new TypeTable() {
            @Override

    checkNotNull(keyFunction);
    while (values.hasNext()) {
      V value = values.next();
      builder.put(keyFunction.apply(value), value);
    }
    try {
      return builder.buildOrThrow();
    } catch (IllegalArgumentException duplicateKeys) {
      throw new IllegalArgumentException(
          duplicateKeys.getMessage()
              + ". To index multiple values under a key, use Multimaps.index.");

    checkNotNull(keyFunction);
    while (values.hasNext()) {
      V value = values.next();
      builder.put(keyFunction.apply(value), value);
    }
    try {
      return builder.buildOrThrow();
    } catch (IllegalArgumentException duplicateKeys) {
      throw new IllegalArgumentException(
          duplicateKeys.getMessage()
              + ". To index multiple values under a key, use Multimaps.index.");