Set default file_reference to b"" instead of None

Author: delivrance

pyrogram/file_id.py

@@ -159,7 +159,7 @@ def __init__(
  minor: int = MINOR,
  file_type: FileType,
  dc_id: int,
- file_reference: bytes = None,
+ file_reference: bytes = b"",
  url: str = None,
  media_id: int = None,
  access_hash: int = None,
@@ -239,7 +239,7 @@ def decode(file_id: str):
  access_hash=access_hash
  )
 
- file_reference = Bytes.read(buffer) if has_file_reference else None
+ file_reference = Bytes.read(buffer) if has_file_reference else b""
  media_id, access_hash = struct.unpack("<qq", buffer.read(16))
 
  if file_type in PHOTO_TYPES: