fix get() with doc_id no results

src/grung/db.py

@@ -51,6 +51,7 @@ class RecordTable(table.Table):
             document = super().get(doc_id=doc_id)
             if document:
                 return document.deserialize(self.db, recurse=recurse)
+            return None
 
         matches = self.search(*args, recurse=recurse, **kwargs)
         if matches:

src/grung/types.py

@@ -343,8 +343,9 @@ class TextFilePointer(BinaryFilePointer):
     extension: str = ".txt"
 
     def prepare(self, data: value_type):
-        if data and not isinstance(data, bytes):
+        if isinstance(data, bytes):
-            return str(data).encode()
+            return data
+        return str(data).encode()
 
     def deserialize(self, value: str, db: TinyDB, recurse: bool = True) -> value_type:
         if not value: