Update NST.py

NST.py

@@ -255,7 +255,7 @@ class Nst(datasets.GeneratorBasedBuilder):
                             metadata_key = f'{audio_file.name.replace(".mp3", "")}_{mic}'
                             audio_bytes = tar.extractfile(audio_file).read()
                             audio_dict = {"bytes": audio_bytes, "path": audio_file.name}
-                            fields = {key: metadata[metadata_key][_METADATA_MAPPING[key]] for key in data_fields}
+                            fields = {key: metadata[metadata_key].get(_METADATA_MAPPING[key], "") for key in data_fields}
                             fields["channels"] = 1
                             fields["file"] = fields["file"].replace(".wav", ".mp3")
                             # Fixing some errors in the metadata