Update in_memory_store.rs

Author: Harshdev098

rust/impls/src/in_memory_store.rs

@@ -288,8 +288,8 @@ impl KvStore for InMemoryBackendImpl {
 		&self, user_token: String, request: ListKeyVersionsRequest,
 	) -> Result<ListKeyVersionsResponse, VssError> {
 		let store_id = request.store_id;
-		let key_prefix = request.key_prefix.unwrap_or_default();
-		let page_token = request.page_token.unwrap_or_default();
+		let key_prefix = request.key_prefix.unwrap_or("".to_string());
+		let page_token = request.page_token.unwrap_or("".to_string());
 		let page_size = request.page_size.unwrap_or(i32::MAX);
 		let limit = std::cmp::min(page_size, LIST_KEY_VERSIONS_MAX_PAGE_SIZE) as usize;
 
@@ -400,4 +400,4 @@ mod tests {
 		let response = store.get(user_token.clone(), global_request).await.unwrap();
 		assert_eq!(response.value.unwrap().version, 0, "Expected global_version=0");
 	}
-}
+}