Major Description
The method
GraphTraversal<S, E> property(final VertexProperty.Cardinality cardinality, final Object key, final Object value, final Object... keyValues)
can be applied to any "current traversal location", whether that's a vertex or an edge. However, if this particular signature is applied to an edge with either (inclusive) cardinality or keyValues specified, it produces a ClassCastException when evaluated at AddPropertyStep.java:151. I understand entirely that multi-properties may not be supported on edges, but inadvertently adding single should, if an error, produce a compile-time error instead of a runtime ClassCastException. (At a minimum, a useful runtime exception should be thrown to indicate the semantic problem.)