Navigation block: prevent error in Firefox when removing the navigation block

[frontdevde]

Description

As described in issue #18356 currently we see an error in Firefox when removing the navigation block. This is caused by a null value which this PR aims to filter out ahead of time.

Fixes #18356

How has this been tested?

• Open latest Firefox
• Add the experimental navigation block
• Try removing it, an error appears.
• Apply this fix
• Try removing it. No error should appear, the block should be deleted.

Screenshots

Click "Remove block" on the navigation block:

Result Before:

Result After:

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR. .

[WunderBart]

Nice catch! I have a newbie question: How does a nil value end up in blocks array? Is there a use-case for it?

[frontdevde]

I'm not sure there is a use case for it and it probably shouldn't end up there. That's something we should look at separately. This PR mainly addresses the fact that it did end up here and we should thus safeguard against that happening.

[marekhrabe]

I can no longer see the "unexpected error" overlay over the editor. The console still shows an error (a different one):

Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in the componentWillUnmount method.
    in SlotComponent (created by Context.Consumer)
    in Slot (created by __experimentalBlockSettingsMenuPluginsExtensionSlot)
    in __experimentalBlockSettingsMenuPluginsExtensionSlot (created by Dropdown)
    in div (created by MenuGroup)
    in div (created by MenuGroup)
    in MenuGroup (created by WithInstanceId(MenuGroup))
    in WithInstanceId(MenuGroup) (created by Dropdown)
    in div (created by NavigableContainer)
    in NavigableContainer (created by ForwardRef(NavigableContainer))
    in ForwardRef(NavigableContainer) (created by ForwardRef(NavigableMenu))
    in ForwardRef(NavigableMenu) (created by Dropdown)
    in div (created by Animate)
    in div (created by IsolatedEventContainer)
    in IsolatedEventContainer (created by Animate)
    in Animate (created by Popover)
    in PopoverDetectOutside (created by WithFocusOutside(PopoverDetectOutside))
    in div (created by WithFocusOutside(PopoverDetectOutside))
    in WithFocusOutside(PopoverDetectOutside) (created by Popover)
    in Unknown (created by FocusReturn)
    in div (created by FocusReturn)
    in FocusReturn (created by Context.Consumer)
    in WithFocusReturn(Component) (created by WithConstrainedTabbing(WithFocusReturn(Component)))
    in div (created by WithConstrainedTabbing(WithFocusReturn(Component)))
    in WithConstrainedTabbing(WithFocusReturn(Component)) (created by Popover)
    in FillComponent (created by Context.Consumer)
    in Fill (created by Context.Consumer)
    in span (created by Context.Consumer)
    in Popover (created by Dropdown)
    in div (created by Dropdown)
    in Dropdown (created by DropdownMenu)
    in DropdownMenu (created by BlockActions)
    in div (created by ToolbarContainer)
    in ToolbarContainer (created by Toolbar)
    in Toolbar (created by BlockActions)
    in BlockActions (created by WithDispatch(BlockActions))
    in WithDispatch(BlockActions)
    in Unknown (created by WithSelect(WithDispatch(BlockActions)))
    in WithSelect(WithDispatch(BlockActions)) (created by BlockSettingsMenu)
    in BlockSettingsMenu (created by BlockToolbar)
    in div (created by BlockToolbar)
    in BlockToolbar
    in Unknown (created by WithSelect(BlockToolbar))
    in WithSelect(BlockToolbar) (created by BlockContextualToolbar)
    in div (created by NavigableContainer)
    in NavigableContainer (created by ForwardRef(NavigableContainer))
    in ForwardRef(NavigableContainer) (created by ForwardRef(NavigableMenu))
    in ForwardRef(NavigableMenu) (created by NavigableToolbar)
    in NavigableToolbar (created by BlockContextualToolbar)
    in BlockContextualToolbar (created by BlockListBlock)
    in div (created by BlockListBlock)
    in div (created by ForwardRef)
    in ForwardRef (created by IgnoreNestedEvents)
    in IgnoreNestedEvents (created by ForwardRef(IgnoreNestedEvents))
    in ForwardRef(IgnoreNestedEvents) (created by BlockListBlock)
    in BlockListBlock
    in Unknown
    in Unknown (created by (BlockListBlock))
    in (BlockListBlock) (created by WithMetaAttributeSource((BlockListBlock)))
    in WithMetaAttributeSource((BlockListBlock)) (created by WithFilters(BlockListBlock))
    in WithFilters(BlockListBlock) (created by IfCondition(WithFilters(BlockListBlock)))
    in IfCondition(WithFilters(BlockListBlock)) (created by WithDispatch(IfCondition(WithFilters(BlockListBlock))))
    in WithDispatch(IfCondition(WithFilters(BlockListBlock)))
    in Unknown (created by WithSelect(WithDispatch(IfCondition(WithFilters(BlockListBlock)))))
    in WithSelect(WithDispatch(IfCondition(WithFilters(BlockListBlock))))
    in Unknown (created by Pure(WithViewportMatch(WithSelect(WithDispatch(IfCondition(WithFilters(BlockListBlock)))))))
    in Pure(WithViewportMatch(WithSelect(WithDispatch(IfCondition(WithFilters(BlockListBlock)))))) (created by BlockList)
    in BlockAsyncModeProvider (created by BlockList)

Considering the original issue is of a well-described scope and this solution fixes it, I'm happy approving this PR. If I can reproduce the other error consistently, I'll file it separately.