fix: Ensure single conduit graphs are initialised correctly

src/conduits/java/com/enderio/conduits/common/network/ConduitSavedData.java

@@ -77,6 +77,13 @@ private ConduitSavedData(Level level, CompoundTag nbt) {
                     ListTag graphObjectsTag = graphTag.getList(KEY_GRAPH_OBJECTS, Tag.TAG_COMPOUND);
                     ListTag graphConnectionsTag = graphTag.getList(KEY_GRAPH_CONNECTIONS, Tag.TAG_COMPOUND);
 
+                    // Skip any graphs which have no objects in them, they should not have been
+                    // saved.
+                    if (graphObjectsTag.isEmpty()) {
+                        // TODO: Warning or something?
+                        continue;
+                    }
+
                     List<ConduitGraphObject<?>> graphObjects = new ArrayList<>();
                     List<Pair<GraphObject<Mergeable.Dummy>, GraphObject<Mergeable.Dummy>>> connections = new ArrayList<>();
 
@@ -94,6 +101,10 @@ private ConduitSavedData(Level level, CompoundTag nbt) {
                         connections.add(new Pair<>(graphObjects.get(connectionTag.getInt("0")), graphObjects.get(connectionTag.getInt("1"))));
                     }
 
+                    // Create a graph for the first object, in case it is a single-node graph
+                    var firstGraphObject = graphObjects.get(0);
+                    Graph.integrate(firstGraphObject, List.of());
+
                     for (ConduitGraphObject<?> graphObject : graphObjects) {
                         // Find neighbors
                         var neighbors = connections
@@ -108,9 +119,21 @@ private ConduitSavedData(Level level, CompoundTag nbt) {
                         }
                     }
 
-                    // Get the graph from the loaded data
-                    var firstGraphObject = graphObjects.get(0);
+                    // Store the resulting graph in our network map.
                     var graph = firstGraphObject.getGraph();
+
+                    // If the graph is null after linking all the objects together, something has
+                    // gone really wrong.
+                    // While we *should* maybe check that there isn't a graph in all places (in case
+                    // of corruption and try to recover)
+                    // it is likely best that we throw this as an error and deal with it once we
+                    // have context for why this could happen (it shouldn't).
+                    if (graph == null) {
+                        EnderIO.LOGGER.error(
+                            "Graph is null after loading a network. Please report this issue to Ender IO, loading cannot continue.");
+                        throw new IllegalStateException("Graph was null after loading the conduit network");
+                    }
+
                     networks.computeIfAbsent(value, ignored -> new ArrayList<>()).add(graph);
                 }
             }