[3.17] [REGRESSION] re-rendering an {{#each}} with multiple null values only renders one iteration

[bendemboski]

When updating an {{#each}}-rendered array to be [ null, null, null ], only one iteration of the array is rendered, as if it just contained [ null ]. This rendering test passes in 3.16 and fails in 3.17:

  test('rerendering array of nulls works', async function(assert) {
    this.set('items', [ false, false, false ]);
    await render(hbs`
      {{#each this.items as |item|}}
        <p>item: {{item}}</p>
      {{/each}}
    `);
    assert.dom('p').exists({ count: 3 });

    this.set('items', [ null, null, null ]);
    await settled();
    assert.dom('p').exists({ count: 3 });
  });

here is an app that reproduces the issue and demonstrates that it's a regression since 3.16.

[pzuraq]

Bugfix submitted upstream, pending review