If $template param is null, means  reset to default value.
 for this test needed
```
	public function testTemplate() {
		$this->CakeEmail->template('template', 'layout');
		$expected = array('template' => 'template', 'layout' => 'layout');
		$this->assertSame($this->CakeEmail->template(), $expected);

		$this->CakeEmail->template('new_template');
		$expected = array('template' => 'new_template', 'layout' => 'layout');
		$this->assertSame($this->CakeEmail->template(), $expected);

		$this->CakeEmail->template('template', null);
		$expected = array('template' => 'template', 'layout' => 'default');
		$this->assertSame($this->CakeEmail->template(), $expected);

		$this->CakeEmail->template(null, null);
		$expected = array('template' => 'default', 'layout' => 'default');
		$this->assertSame($this->CakeEmail->template(), $expected);
	}
```