Empty storages should now return None and not raise ValueError (see #67)

docs/extend.rst

@@ -54,10 +54,11 @@ of course you can add your own. Let's look how you could add a
 
         def read(self):
             with open(self.filename) as handle:
-                data = yaml.safe_load(handle.read())  # (2)
-
-            if data is None:  # (3)
-                raise ValueError
+                try:
+                    data = yaml.safe_load(handle.read())  # (2)
+                    return data
+                except yaml.YAMLError:
+                    return None  # (3)
 
         def write(self, data):
             with open(self.filename, 'w') as handle:
@@ -75,8 +76,8 @@ There are some things we should look closer at:
 2. We use ``yaml.safe_load`` as recommended by the
    `PyYAML documentation <http://pyyaml.org/wiki/PyYAMLDocumentation#LoadingYAML>`_
    when processing data from a potentially untrusted source.
-3. If the storage is uninitialized, TinyDB expects the storage to throw a
-   ``ValueError`` so it can do any internal initialization that is necessary.
+3. If the storage is uninitialized, TinyDB expects the storage to return
+   ``None`` so it can do any internal initialization that is necessary.
 4. If your storage needs any cleanup (like closing file handles) before an
    instance is destroyed, you can put it in the ``close()`` method. To run
    these, you'll either have to run ``db.close()`` on your ``TinyDB`` instance

tinydb/database.py

@@ -99,10 +99,7 @@ def _read(self):
         :rtype: dict
         """
 
-        try:
-            return self._storage.read()
-        except ValueError:
-            return {}
+        return self._storage.read() or {}
 
     def _read_table(self, table):
         """

tinydb/middlewares.py

@@ -155,6 +155,9 @@ def register_serializer(self, serializer, name):
     def read(self):
         data = self.storage.read()
 
+        if data is None:
+            return None
+
         for serializer_name in self._serializers:
             serializer = self._serializers[serializer_name]
             tag = '{{{0}}}:'.format(serializer_name)  # E.g: '{TinyDate}:'

tinydb/storages.py

@@ -37,7 +37,7 @@ def read(self):
         Read the last stored state.
 
         Any kind of deserialization should go here.
-        Raise ``ValueError`` here to indicate that the storage is empty.
+        Return ``None`` here to indicate that the storage is empty.
 
         :rtype: dict
         """
@@ -93,8 +93,16 @@ def __del__(self):
         self.close()
 
     def read(self):
-        self._handle.seek(0)
-        return json.load(self._handle)
+        # Get the file size
+        self._handle.seek(0, 2)
+        size = self._handle.tell()
+
+        if not size:
+            # File is empty
+            return None
+        else:
+            self._handle.seek(0)
+            return json.load(self._handle)
 
     def write(self, data):
         self._handle.seek(0)
@@ -118,8 +126,6 @@ def __init__(self):
         super(MemoryStorage, self).__init__()
 
     def read(self):
-        if self.memory is None:
-            raise ValueError
         return self.memory
 
     def write(self, data):