src/Field.php
public function guardValue($value)
    {
        if ($this->required) {
            Assertion::notNull($value, sprintf('Field [%s] is required and cannot be null.', $this->name));
        }

        if (null !== $value) {
            $this->type->guard($value, $this);
        }

        if (null !== $this->assertion) {
            call_user_func($this->assertion, $value, $this);
        }
    }
public function guardValue($value)
    {
        if ($this->required) {
            Assertion::notNull($value, sprintf('Field [%s] is required and cannot be null.', $this->name));
        }

        if (null !== $value) {
            $this->type->guard($value, $this);
        }

        if (null !== $this->assertion) {
            call_user_func($this->assertion, $value, $this);
        }
    }
@param mixed $value

@throws AssertionFailed
@throws \Exception