Add error message for empty string in filedataloader.

Differential Revision: D72981574

Pull Request resolved: pytorch#10145

Author: JacobSzwejbka

extension/data_loader/file_data_loader.cpp

@@ -86,6 +86,9 @@ Result<FileDataLoader> FileDataLoader::from(
       "Alignment %zu is not a power of 2",
       alignment);
 
+  ET_CHECK_OR_RETURN_ERROR(
+      file_name != nullptr, InvalidArgument, "File name cannot be empty.");
+
   // Use open() instead of fopen() to avoid the layer of buffering that
   // fopen() does. We will be reading large portions of the file in one shot,
   // so buffering does not help.

extension/data_loader/test/file_data_loader_test.cpp

@@ -154,6 +154,12 @@ TEST_P(FileDataLoaderTest, FromMissingFileFails) {
   EXPECT_NE(fdl.error(), Error::Ok);
 }
 
+TEST_P(FileDataLoaderTest, FromEmptyFilePathFails) {
+  // Nullptr should fail
+  Result<FileDataLoader> fdl = FileDataLoader::from(nullptr);
+  EXPECT_NE(fdl.error(), Error::Ok);
+}
+
 TEST_P(FileDataLoaderTest, BadAlignmentFails) {
   // Create a temp file; contents don't matter.
   uint8_t data[256] = {};