What should be the expected behavior when I call MPI_IRecv/MPI_Recv when there're no messages

I'm new to MPI so bear with me. I could find any documents on what the expected behavior is in this case.

Let's say I have proc #1 calling MPI_IRecv from ANY_SOURCE but no one has ever sent anything to proc #1, would I receive an empty buffer or would I get an error?