Bulk loader: do not fail on empty files

lib/src/storage/backend/rocksdb.rs

@@ -814,6 +814,9 @@ impl Db {
         &self,
         ssts_for_cf: &[(&ColumnFamily, PathBuf)],
     ) -> Result<(), StorageError> {
+        if ssts_for_cf.is_empty() {
+            return Ok(()); // Rocksdb does not support empty lists
+        }
         if let DbKind::ReadWrite(db) = &self.inner {
             let mut paths_by_cf = HashMap::<_, Vec<_>>::new();
             for (cf, path) in ssts_for_cf {

lib/tests/store.rs

@@ -12,6 +12,8 @@ use std::fs::{create_dir, remove_dir_all, File};
 use std::io::Cursor;
 #[cfg(not(target_family = "wasm"))]
 use std::io::Write;
+#[cfg(not(target_family = "wasm"))]
+use std::iter::empty;
 #[cfg(target_os = "linux")]
 use std::iter::once;
 #[cfg(not(target_family = "wasm"))]
@@ -159,6 +161,16 @@ fn test_bulk_load_graph_lenient() -> Result<(), Box<dyn Error>> {
     Ok(())
 }
 
+#[test]
+#[cfg(not(target_family = "wasm"))]
+fn test_bulk_load_empty() -> Result<(), Box<dyn Error>> {
+    let store = Store::new()?;
+    store.bulk_loader().load_quads(empty::<Quad>())?;
+    assert!(store.is_empty()?);
+    store.validate()?;
+    Ok(())
+}
+
 #[test]
 fn test_load_dataset() -> Result<(), Box<dyn Error>> {
     let store = Store::new()?;