I'm not very fund of the subject, but what i know is that the Schwarzschild metric and other known solutions for Einstein's action have some constant representing mass. However, I encountered some solutions where no such constant existed. Can someone explain to me what does this mean exactly? In fact, does it mean that there is no mass in the geometry? and if so, how do we get a curved space-time when general relativity states that the curvature is determined by the distribution of mass?