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psalm/docs/running_psalm/issues/PossiblyUndefinedArrayOffset.md

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# PossiblyUndefinedArrayOffset
Emitted when trying to access a possibly undefined array offset
```php
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<?php
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if (rand(0, 1)) {
$arr = ["a" => 1, "b" => 2];
} else {
$arr = ["a" => 3];
}
echo $arr["b"];
```
## How to fix
You can use the null coalesce operator to provide a default value in the event the array offset does not exist:
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```php
<?php
...
echo $arr["b"] ?? 0;
```
Alternatively, you can ensure that the array offset always exists:
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```php
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<?php
if (rand(0, 1)) {
$arr = ["a" => 1, "b" => 2];
} else {
$arr = ["a" => 3, "b" => 0];
}
echo $arr["b"];
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```