diff --git a/sbe/__init__.py b/sbe/__init__.py
index cc1cf58..d5d1cef 100644
--- a/sbe/__init__.py
+++ b/sbe/__init__.py
@@ -107,6 +107,8 @@ def __init__(self, name: str, primitiveType: PrimitiveType, nullValue: Optional[
                 self.nullValue = float(nullValue)
             else:
                 self.nullValue = int(nullValue)
+        else:
+            self.nullValue = None
 
     def __repr__(self):
         rv = self.name + " ("
@@ -277,7 +279,8 @@ class Set:
 
     def encode(self, vals: Iterable[str]) -> int:
         vals = set(vals)
-        return bitstring.BitArray(v.name in vals for i, v in enumerate(self.choices)).uint
+        assert vals.issubset({c.name for c in self.choices}), f"{vals} is not a subset of {self.choices}"
+        return bitstring.BitArray(v.name in vals for v in reversed(self.choices)).uint
 
     def decode(self, val: int) -> List[str]:
         if isinstance(self.encodingType, SetEncodingType):
@@ -496,7 +499,8 @@ def encode(self, message: Message, obj: dict, header: Optional[dict] = None) ->
         fmts = []
         vals = []
         cursor = Cursor(0)
-        _walk_fields_encode(self, message.fields, obj, fmts, vals, cursor)
+        _walk_fields_encode(self, message.fields, obj, fmts, vals,
+                            message.blockLength, cursor)
         fmt = "<" + ''.join(fmts)
 
         header = {
@@ -696,6 +700,8 @@ def _prettify_type(_schema: Schema, t: Type, v):
         t.characterEncoding == CharacterEncoding.ASCII or t.characterEncoding is None
     ):
         return v.split(b'\x00', 1)[0].decode('ascii', errors='ignore').strip()
+    if t.nullValue is not None and v == t.nullValue:
+        return None
 
     return v
 
@@ -737,16 +743,22 @@ def _walk_fields_encode_composite(
                 cursor.val += FORMAT_SIZES[t1]
 
 
-def _walk_fields_encode(schema: Schema, fields: List[Union[Group, Field]], obj: dict, fmt: list, vals: list, cursor: Cursor):
+def _walk_fields_encode(schema: Schema, fields: List[Union[Group, Field]],
+                        obj: dict, fmt: list, vals: list, blockLength: int,
+                        cursor: Cursor):
     for f in fields:
         if isinstance(f, Group):
+            if cursor.val < blockLength:
+                fmt.append(str(blockLength - cursor.val) + 'x')
+                cursor.val = blockLength
             xs = obj[f.name]
 
             fmt1 = []
             vals1 = []
             block_length = None
             for x in xs:
-                _walk_fields_encode(schema, f.fields, x, fmt1, vals1, Cursor(0))
+                _walk_fields_encode(schema, f.fields, x, fmt1, vals1,
+                                    f.blockLength, Cursor(0))
                 if block_length is None:
                     block_length = struct.calcsize("<" + ''.join(fmt1))
 
diff --git a/tests/dat/example-schema.xml b/tests/dat/example-schema.xml
index b4a39e7..746e7d7 100644
--- a/tests/dat/example-schema.xml
+++ b/tests/dat/example-schema.xml
@@ -14,6 +14,7 @@
         <type name="Ron" primitiveType="uint8" minValue="90" maxValue="110"/>
         <type name="someNumbers" primitiveType="uint32" length="4"/>
         <type name="Percentage" primitiveType="int8" minValue="0" maxValue="100"/>
+        <type name="IntNULL" primitiveType="uint16" nullValue="65535"/>
         <composite name="Booster">
             <enum name="BoostType" encodingType="char">
                 <validValue name="TURBO">T</validValue>
@@ -74,4 +75,13 @@
         <data name="model" id="19" type="varStringEncoding"/>
         <data name="activationCode" id="20" type="varAsciiEncoding"/>
     </sbe:message>
+    <sbe:message name="TestNullValue" id="2">
+        <field name="nullable" id="1" type="IntNULL"/>
+    </sbe:message>
+    <sbe:message name="TestBlockLength" id="3" blockLength="4">
+        <field name="year" id="1" type="ModelYear"/>
+        <group name="AGroup" id="2" dimensionType="groupSizeEncoding" blbockLength="6">
+            <field name="numbers" id="1" type="someNumbers"/>
+        </group>
+    </sbe:message>
 </sbe:messageSchema>
diff --git a/tests/test_sbe.py b/tests/test_sbe.py
index c92f601..61e28ce 100644
--- a/tests/test_sbe.py
+++ b/tests/test_sbe.py
@@ -7,3 +7,33 @@ def test_parse1():
 def test_parse2():
     with open('tests/dat/b3-entrypoint-messages-8.0.0.xml', 'r') as f:
         sbe.Schema.parse(f)
+
+def test_nullValue():
+    with open('tests/dat/example-schema.xml', 'r') as f:
+        s = sbe.Schema.parse(f)
+        nullable = s.messages[2]
+
+        encodedInt = s.encode(nullable, {'nullable': 5})
+        decodedInt = s.decode(encodedInt)
+        assert decodedInt.value['nullable'] == 5
+
+        encodedNull = s.encode(nullable, {'nullable': None})
+        decodedNull = s.decode(encodedNull)
+        assert decodedNull.value['nullable'] is None
+
+def test_blockLength():
+    with open('tests/dat/example-schema.xml', 'r') as f:
+        s = sbe.Schema.parse(f)
+        msg  = s.messages[3]
+
+        encoded = s.encode(msg, {'year': 1990, 'AGroup': [{'numbers': 123},
+                                                          {'numbers': 456}]})
+        # BlockHeader = 8b
+        # Body = 2b year + 2b padding
+        # Repeating group = 2 * (4b numbers + 2b padding)
+        expLen = 8 + 4 + 2*6
+        assert len(encoded) == expLen, "Encoded SBE not padded properly"
+
+        decoded  = s.decode(encoded)
+        assert decoded.value['year'] == 1990
+        assert decoded.value['AGroup'][1]['numbers'] == 456