WARWICK, R.I. — A unidentified woman robbed a Sunoco gasoline station of an undermined about of cash early Sunday morning, police said.The woman entered the gas station at 2003 Post Road at 2:49 a.m., police said, brandished a knife at the clerk and demanded money. The clerk complied, police said, and the woman was last seen fleeing south in a vehicle on Post Road.Police did not yet have description of the woman Sunday morning.