src/Concerns/HasDocumentAssertions.php
public function assertNull(string $pointer = '/data', string $message = ''): self
    {
        Assert::assertNull($this, $pointer, $message);

        return $this;
    }
public function assertNull(string $pointer = '/data', string $message = ''): self
    {
        Assert::assertNull($this, $pointer, $message);

        return $this;
    }
Assert that the member contains a null value.

@param string $pointer
@param string $message
@return $this