參考網址：question2answer
Before PHP 8.1:
echo strlen(null); // No deprecation notice is shown up. // -> 0
As of PHP 8.1:
echo strlen(null); // Deprecated: strlen(): Passing null to parameter #1 ($string) of type string is deprecated in ... on line ... // -> 0
Solution
The RFC describing this issue is really helpful for possible resolutions and I highly recommend reviewing it. As of Question2Answer, the official resolution was to make use of the Null Coalescing Operator (??) when possible; here is an example from GitHub, which replaces:
if (strlen($error )) {...}
with this:
if (strlen($error ?? '')) {...}
This effectively fixes the issue.
合併運算子(??)
php7開始支援