public static function dropCache($key = null)
    {
        if ($key !== null && isset(static::$_cache[$key])) {
            unset(static::$_cache[$key]);
        } else {
            static::$_cache = [];
        }
    }
public static function dropCache($key = null)
    {
        if ($key !== null && isset(static::$_cache[$key])) {
            unset(static::$_cache[$key]);
        } else {
            static::$_cache = [];
        }
    }
public static function dropCache ( $ key = null ) { if ( $ key !== null && isset ( static :: $ _cache [ $ key ] ) ) { unset ( static :: $ _cache [ $ key ] ) ; } else { static :: $ _cache = [ ] ; } }
Drops the entire cache or a specific key.

## Usage:

```php
static::dropCache('user_cache'); // removes "user_cache" only
static::dropCache(); // removes every key
```

@param string|null $key Cache key to clear, if NULL the entire cache
will be erased.
@return void
Drops the entire cache or a specific key .