fatal error: unexpectedly found nil while unwrapping an Optional value - swift 3 : <p>my question isn't duplicate because I read them before.</p>

<p>my code:</p>

<pre><code>var str_images = "http://kashanmap.ir/images/apk_images/off/33/Cta_off _1_.jpg ,http://kashanmap.ir/images/apk_images/off/33/Cta_off _2_.jpg ,http://kashanmap.ir/images/apk_images/off/33/Cta_off-_4_.jpg"

    for one_img in multi_img{
        print("one: \(one_img)")
        var img = one_img

        //self.imgs_slider.append(img)
        let alamofireSource = AlamofireSource(urlString: img)!
        images.append(alamofireSource)
    }
</code></pre>

<p>my console log:</p>

<pre><code>one: http://kashanmap.ir/images/apk_images/off/33/Cta_off _1_.jpg 
fatal error: unexpectedly found nil while unwrapping an Optional value
(lldb) 
</code></pre>

<p><a href="https://i.stack.imgur.com/xgVYA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xgVYA.png" alt="enter image description here"></a></p>

<p>I changed this line:</p>

<pre><code>        var img = one_img
</code></pre>

<p>to:</p>

<pre><code>        var img = one_img?
</code></pre>

<p>or</p>

<pre><code>        var img = one_img!
</code></pre>

<p>but Xcode shows a red cycle to remove <code>?</code> or <code>!</code> . </p>
