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So we used this catch-all feature here,

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but currently there is one problem,

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if you wanna call it like this.

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Whenever we enter something invalid here,

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like too many POV segments, we see that fall back text.

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Now that's actually not necessarily a problem.

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We might be fine with that,

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but we also might want to actually show an error

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instead if invalid POV segments were entered here.

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and we could implement this

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by going back to the page.js file here.

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And then, right before returning this content,

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this JSX content, we could add a if check

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and check if we have a selected year

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and the available news years

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do not include this selected year.

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So the available news years will give us an array.

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Do not include the selected year,

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which we check by using the includes method

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and adding an exclamation mark in front of this.

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So now if we have a selected year,

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but it's not part of the available years,

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we'll make it into this if block.

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And in here, I want to throw a new error

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where I'll say "invalid filter."

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And that's not the only way of ending up

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with an invalid filter.

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Because besides this condition,

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there also is another alternative condition

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that should throw an error.

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So I'll add a logical or here

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and then I'll check if we maybe have a selected month

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and that selected month is not part of the available months.

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So if not get available news months

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and we have to pass the selected year to the news month,

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if that array does not include the selected month,

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that's the alternative condition.

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So if one of these two conditions,

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this condition or this condition,

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if one of these two conditions is met,

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we make it in there and throw an error.

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And actually here we have to be careful

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because the years and months,

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these utility functions will return,

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will actually be of type number.

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So we'll get back numbers here.

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Whereas the selected years

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and months which we extract from the path,

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the URL path will be of type string.

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Here it says any. but it will be strings.

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And includes therefore would actually return false

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since we have a type mismatch,

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even if it's the same kind of value that's stored.

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So we should actually convert selected year to a number here

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and also selected month here

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to make sure that we don't get an error in situations

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where we shouldn't get it.

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But with those changes made, you'll see that if you visit,

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for example, a valid year, that works.

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If you visit a valid year-month combination, that works.

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But if I enter invalid month,

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I get this default development mode error overlay.

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And if I enter some arbitrary paths,

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potentially also too many POV segments,

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I also get this error overlay.

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Now of course,

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I don't want to get that development error overlay,

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but instead my own error page

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and therefore, we should now also add error handling here.