diff --git a/api/server/router/system/system_routes.go b/api/server/router/system/system_routes.go
index 27063fc0ff664ebd0b19e5c3bbf669c55408b41b..246cc67415c968ba9d56ef9c11a491c5503326da 100644
--- a/api/server/router/system/system_routes.go
+++ b/api/server/router/system/system_routes.go
@@ -120,6 +120,11 @@ func (s *systemRouter) getDiskUsage(ctx context.Context, w http.ResponseWriter,
 
 	du.BuilderSize = builderSize
 	du.BuildCache = buildCache
+	if buildCache == nil {
+		// Ensure empty `BuildCache` field is represented as empty JSON array(`[]`)
+		// instead of `null` to be consistent with `Images`, `Containers` etc.
+		du.BuildCache = []*types.BuildCache{}
+	}
 
 	return httputils.WriteJSON(w, http.StatusOK, du)
 }
diff --git a/api/swagger.yaml b/api/swagger.yaml
index 40beae7a32a4dedf04ece09ecc27c977bf63117a..ddb8544bccdff2d56f6bb7addf754a090858ebd6 100644
--- a/api/swagger.yaml
+++ b/api/swagger.yaml
@@ -8339,6 +8339,7 @@ paths:
                   UsageData:
                     Size: 10920104
                     RefCount: 2
+              BuildCache: []
         500:
           description: "server error"
           schema: