Only One Border for Flex Image Grid Cells via CSS

I have a flexbox grid of images and I'm trying to only add one border to each of the cells — the challenge is that this is a grid that will continue to have images added to it, so I'll never know exactly how many images/cells there will be. I'm trying to accomplish this via CSS alone. My code:

* {
  box-sizing: border-box;
}

.container {
  display: flex;
  flex-wrap: wrap;
  padding: 5px;
}

.item {
  padding: 5px;
}

<div class="container">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
</div>

The obvious challenge is to avoid the double borders something like this would inevitably create on the class .item:

border: 1px solid #000;

And not knowing in advance how many images there will be in the grid means I can't use something like :nth-of-type(xn) to remove or add borders. Thanks for any help you can provide here.

Solution

Slightly hacky, but using a negative left and top margin of 1 pixel will cover the double border.

* {
  box-sizing: border-box;
}

.container {
  display: inline-flex;
  flex-wrap: wrap;
  padding: 5px;
}

.item {
  border: 1px solid #000;
  padding: 5px;
  margin: -1px 0 0 -1px;
}

<div class="container">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
  <img class="item" src="https://via.placeholder.com/150x100" alt="Example image">
</div>