Avoid using enum = null for older flatc versions (ubuntu 22.04)

schema/lrs.fbs

@@ -52,14 +52,14 @@ table Node {
     connections:[Connection] (required);
 }
 
-enum Endpoint : byte { Begin = 1, End = 2 }
+enum Endpoint : byte { Unknown = 0, Begin = 1, End = 2 }
 /// A connection links a node to a segment
 table Connection {
     properties:[Property];
 
     segment_index:uint64;
     /// A segment is oriented. The endpoint indicates what end of the segment is connected to the node
-    endpoint:Endpoint = null;
+    endpoint:Endpoint;
 }
 
 ///  A traversal is a path in a network.
@@ -143,7 +143,7 @@ enum GeometryType : byte { Geographic = 1, Schematic = 2 }
 table GeometryView {
     properties:[Property];
 
-    geometry_type:GeometryType = null;
+    geometry_type:GeometryType = Geographic;
     anchors:[AnchorGeometry] (required);
     /// Must be the same size as the top level network array
     networks:[NetworkGeometry] (required);