diff --git a/internal/httpapi/api_test.go b/internal/httpapi/api_test.go
index 692ba44..c59f0a2 100644
--- a/internal/httpapi/api_test.go
+++ b/internal/httpapi/api_test.go
@@ -263,6 +263,20 @@ func TestAPIEndToEnd(t *testing.T) {
 		}
 	})
 
+	// Regression: rel_type is an optional array param (*[]string); when
+	// omitted entirely (not an empty list), passing the nil pointer straight
+	// through to pgx as a query arg panics because pgx can't infer the array
+	// element type from a nil *[]string. root+depth alone must still work.
+	t.Run("graph without rel_type", func(t *testing.T) {
+		rec, body := get(t, h, "/api/v1/graph?root=host:hubris&depth=1", nil)
+		if rec.Code != 200 {
+			t.Fatalf("status %d", rec.Code)
+		}
+		if len(body["nodes"].([]any)) < 2 {
+			t.Errorf("graph too small: %d nodes", len(body["nodes"].([]any)))
+		}
+	})
+
 	t.Run("ontology", func(t *testing.T) {
 		rec, body := get(t, h, "/api/v1/ontology", nil)
 		if rec.Code != 200 {
diff --git a/internal/httpapi/impl.go b/internal/httpapi/impl.go
index 80a9cb1..9203337 100644
--- a/internal/httpapi/impl.go
+++ b/internal/httpapi/impl.go
@@ -211,7 +211,7 @@ func (s *Server) GetEntityRelations(ctx context.Context, req gen.GetEntityRelati
 			Type:       r.Type,
 			Attributes: attrs,
 			ValidFrom:  r.ValidFrom,
-			ValidTo:     validTo,
+			ValidTo:    validTo,
 		})
 	}
 	return gen.GetEntityRelations200JSONResponse{Items: items}, nil
@@ -282,6 +282,15 @@ func (s *Server) GetGraph(ctx context.Context, req gen.GetGraphRequestObject) (g
 	var err error
 	truncated := false
 
+	// pgx can't infer the array element type from a nil *[]string (the
+	// param is absent from the request, not an empty list), so dereference
+	// to a plain []string first — nil there still encodes as SQL NULL, but
+	// pgx has a concrete type to work with.
+	var relTypes []string
+	if req.Params.RelType != nil {
+		relTypes = *req.Params.RelType
+	}
+
 	if req.Params.Root != nil && *req.Params.Root != "" {
 		rootID, rerr := s.resolveEntityID(ctx, *req.Params.Root)
 		if rerr != nil {
@@ -291,7 +300,7 @@ func (s *Server) GetGraph(ctx context.Context, req gen.GetGraphRequestObject) (g
 			SELECT `+entityCols+`
 			FROM blast_radius($1, $2, $3) b JOIN entities e ON e.id = b.entity_id
 			LEFT JOIN entity_status st ON st.entity_id = e.id
-			ORDER BY e.slug`, rootID, depth, req.Params.RelType)
+			ORDER BY e.slug`, rootID, depth, relTypes)
 	} else {
 		// Whole-graph view: pick the most-connected entities first so the
 		// graph shows actual topology, not just whatever sorts first
@@ -327,7 +336,7 @@ func (s *Server) GetGraph(ctx context.Context, req gen.GetGraphRequestObject) (g
 	}
 	edgeRows, err := sqlcgen.New(s.pool).ListGraphEdges(ctx, sqlcgen.ListGraphEdgesParams{
 		Ids:      ids,
-		RelTypes: *req.Params.RelType,
+		RelTypes: relTypes,
 	})
 	if err != nil {
 		return nil, err
@@ -348,7 +357,7 @@ func (s *Server) GetGraph(ctx context.Context, req gen.GetGraphRequestObject) (g
 			Type:       r.Type,
 			Attributes: attrs,
 			ValidFrom:  r.ValidFrom,
-			ValidTo:     validTo,
+			ValidTo:    validTo,
 		})
 	}