adder.accept(accumulator, SomeEnum.B);
    ImmutableSet<SomeEnum> set = collector.finisher().apply(accumulator);
    assertThat(set).containsExactly(SomeEnum.A, SomeEnum.B);

    // Subsequent manual manipulation of the accumulator must not affect the state of the built set
    adder.accept(accumulator, SomeEnum.C);
    assertThat(set).containsExactly(SomeEnum.A, SomeEnum.B);
  }

  @J2ktIncompatible

 @include border-right-radius(0);\n  }\n\n  > .btn:not(:first-child),\n  > .btn-group:not(:first-child) > .btn {\n    @include border-left-radius(0);\n  }\n}\n\n// Sizing\n//\n// Remix the default button sizing classes into new ones for easier manipulation.\n\n.btn-group-sm > .btn { @extend .btn-sm; }\n.btn-group-lg > .btn { @extend .btn-lg; }\n\n\n//\n// Split button dropdowns\n//\n\n.dropdown-toggle-split {\n  padding-right: $btn-padding-x * .75;\n  padding-left: $btn-padding-x * .75;\n\n  &::after,\n...

direction different from `right`\n     */\n    y: 'right',\n  },\n\n  /**\n   * Applies the computed styles to the popper element.\n   *\n   * All the DOM manipulations are limited to this modifier. This is useful in case\n   * you want to integrate Popper.js inside a framework or view library and you\n   * want to delegate all the DOM manipulations to it.\n   *\n   * Note that if you disable this modifier, you must make sure the popper element\n   * has its position set to `absolute` before Popper.js...

 @include border-right-radius(0);\n  }\n\n  > .btn:not(:first-child),\n  > .btn-group:not(:first-child) > .btn {\n    @include border-left-radius(0);\n  }\n}\n\n// Sizing\n//\n// Remix the default button sizing classes into new ones for easier manipulation.\n\n.btn-group-sm > .btn { @extend .btn-sm; }\n.btn-group-lg > .btn { @extend .btn-lg; }\n\n\n//\n// Split button dropdowns\n//\n\n.dropdown-toggle-split {\n  padding-right: $btn-padding-x * .75;\n  padding-left: $btn-padding-x * .75;\n\n  &::after,\n...