Ensure network policy conversion round trips nil from field

pkg/apis/extensions/v1beta1/conversion.go

@@ -338,12 +338,14 @@ func Convert_v1beta1_NetworkPolicyIngressRule_To_networking_NetworkPolicyIngress
 			return err
 		}
 	}
+	if in.From != nil {
 		out.From = make([]networking.NetworkPolicyPeer, len(in.From))
 		for i := range in.From {
 			if err := Convert_v1beta1_NetworkPolicyPeer_To_networking_NetworkPolicyPeer(&in.From[i], &out.From[i], s); err != nil {
 				return err
 			}
 		}
+	}
 	return nil
 }
 
@@ -354,12 +356,14 @@ func Convert_networking_NetworkPolicyIngressRule_To_v1beta1_NetworkPolicyIngress
 			return err
 		}
 	}
+	if in.From != nil {
 		out.From = make([]extensionsv1beta1.NetworkPolicyPeer, len(in.From))
 		for i := range in.From {
 			if err := Convert_networking_NetworkPolicyPeer_To_v1beta1_NetworkPolicyPeer(&in.From[i], &out.From[i], s); err != nil {
 				return err
 			}
 		}
+	}
 	return nil
 }