Nelmio\SecurityBundle\ContentSecurityPolicy\DirectiveSet::setDirective PHP Method

    public function setDirective($name, $value)
    {
        $this->checkDirectiveName($name);
        if (self::$directiveNames[$name] === self::TYPE_NO_VALUE) {
            if ($value) {
                $this->directiveValues[$name] = true;
            } else {
                unset($this->directiveValues[$name]);
            }
        } elseif ($value) {
            $this->directiveValues[$name] = $value;
        } else {
            unset($this->directiveValues[$name]);
        }
    }

 public function testDirectiveSetUnset()
 {
     $directiveSet = new DirectiveSet();
     $directiveSet->setDirectives(array('default-src' => 'foo'));
     $this->assertEquals('default-src foo', $directiveSet->buildHeaderValue());
     $directiveSet->setDirective('default-src', '');
     $this->assertEquals('', $directiveSet->buildHeaderValue());
 }