src/Airbrake/Record.php
public function set($key, $value)
    {
        if ($this->exists($key)) {
            $this->dataStore[$key] = $value;
        }
    }
public function set($key, $value)
    {
        if ($this->exists($key)) {
            $this->dataStore[$key] = $value;
        }
    }
Set the given value to the given key.

The given key should match one of the parameters about, but with out the
prefix. That is added on during this process.

@param string $key
@param mixed $value