In edgar allan poe’s “the raven,” what does the speaker see when he responds to the raven’s tapping by opening the door?

When he answers the door, the speaker sees nothing. He does not know the raven is the one tapping at the chamber door. In fact, he believes it is a visitor. However, when he opens the door, he sees "darkness there and nothing more." The stanza states:

Presently my soul grew stronger; hesitating then no longer,

“Sir,” said I, “or Madam, truly your forgiveness I implore;

But the fact is I was napping, and so gently you came rapping,

And so faintly you came tapping, tapping at my chamber door,

That I scarce was sure I heard you”—here I opened wide the door;—

Darkness there and nothing more.