refine dockerfile (#1801)

### What problem does this PR solve?


### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

graphrag/leiden.py

@@ -25,6 +25,7 @@ from graspologic.partition import hierarchical_leiden
 from graspologic.utils import largest_connected_component
 
 import networkx as nx
+from networkx import is_empty
 
 log = logging.getLogger(__name__)
 
@@ -91,13 +92,14 @@ def _compute_leiden_communities(
         seed=0xDEADBEEF,
 ) -> dict[int, dict[str, int]]:
     """Return Leiden root communities."""
+    results: dict[int, dict[str, int]] = {}
+    if is_empty(graph): return results
     if use_lcc:
         graph = stable_largest_connected_component(graph)
 
     community_mapping = hierarchical_leiden(
         graph, max_cluster_size=max_cluster_size, random_seed=seed
     )
-    results: dict[int, dict[str, int]] = {}
     for partition in community_mapping:
         results[partition.level] = results.get(partition.level, {})
         results[partition.level][partition.node] = partition.cluster