Fix client-graph-world npe

Author: Kneelawk

changelogs/changelog-v2.0.2+1.21.md

@@ -0,0 +1,3 @@
+Changes:
+
+* Fixed client-sided graph worlds throwing NPEs when trying to get a graph at an empty block-pos.

modules/syncing-core-xplat/src/main/java/com/kneelawk/graphlib/syncing/impl/graph/simple/SimpleClientGraphWorld.java

@@ -30,11 +30,6 @@
 import java.util.stream.LongStream;
 import java.util.stream.Stream;
 
-import net.minecraft.core.BlockPos;
-import net.minecraft.core.SectionPos;
-import net.minecraft.world.level.ChunkPos;
-import net.minecraft.world.level.Level;
-
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -44,6 +39,11 @@
 import it.unimi.dsi.fastutil.longs.LongLinkedOpenHashSet;
 import it.unimi.dsi.fastutil.longs.LongSet;
 
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.SectionPos;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.Level;
+
 import com.kneelawk.graphlib.api.graph.BlockGraph;
 import com.kneelawk.graphlib.api.graph.GraphUniverse;
 import com.kneelawk.graphlib.api.graph.GraphView;
@@ -187,7 +187,10 @@ public boolean linkExistsAt(@NotNull LinkPos pos) {
         SimpleBlockGraphChunk chunk = manager.getIfExists(SectionPos.of(pos));
         if (chunk == null) return LongStream.empty();
 
-        return chunk.getGraphsAt(pos).longStream();
+        LongSet graphsAt = chunk.getGraphsAt(pos);
+        if (graphsAt == null) return LongStream.empty();
+
+        return graphsAt.longStream();
     }
 
     @Override