diff --git a/tests/test_leadership.py b/tests/test_leadership.py
index f2a8f9b..2bbdc3b 100644
--- a/tests/test_leadership.py
+++ b/tests/test_leadership.py
@@ -988,6 +988,19 @@ async def test_follower_not_multi():
     assert not await list_sessions()
 
 
+@pytest.mark.asyncio
+async def test_follower_force_store_value_none():
+    ip_admin_eth0 = IPOption('ip_admin_eth0', "ip réseau autorisé", multi=True, default=['1.1.1.1'])
+    netmask_admin_eth0 = NetmaskOption('netmask_admin_eth0', "masque du sous-réseau",  multi=True, properties=('force_store_value',))
+    interface0 = Leadership('interface0', '', [ip_admin_eth0, netmask_admin_eth0])
+    od1 = OptionDescription('od', '', [interface0])
+    od2 = OptionDescription('toto', '', [od1])
+    async with await Config(od2) as cfg:
+        await cfg.property.read_write()
+        assert await cfg.option('od.interface0.netmask_admin_eth0', 0).owner.isdefault()
+    assert not await list_sessions()
+
+
 @pytest.mark.asyncio
 async def test_follower_force_store_value():
     ip_admin_eth0 = IPOption('ip_admin_eth0', "ip réseau autorisé", multi=True, default=['1.1.1.1'])
diff --git a/tests/test_option_callback.py b/tests/test_option_callback.py
index b31a50c..bed5273 100644
--- a/tests/test_option_callback.py
+++ b/tests/test_option_callback.py
@@ -1529,6 +1529,34 @@ async def test_calc_value_join(config_type):
     assert not await list_sessions()
 
 
+@pytest.mark.asyncio
+async def test_calc_value_join_multi(config_type):
+    val1 = StrOption('val1', "", multi=True)
+    val4 = StrOption('val4', "", Calculation(calc_value, Params((ParamOption(val1)), join=ParamValue('.'), multi=ParamValue(True))), multi=True)
+    od = OptionDescription('root', '', [val1, val4])
+    async with await Config(od) as cfg:
+        cfg = await get_config(cfg, config_type)
+        assert await cfg.value.dict() == {'val1': [], 'val4': []}
+        await cfg.option('val1').value.set(['val1'])
+        assert await cfg.value.dict() == {'val1': ['val1'], 'val4': ['val1']}
+    assert not await list_sessions()
+
+
+@pytest.mark.asyncio
+async def test_calc_value_join_multi_value(config_type):
+    val1 = StrOption('val1', "", ['val1'], multi=True)
+    val2 = StrOption('val2', "", ['val2'], multi=True)
+    val3 = StrOption('val3', "", [None], multi=True)
+    val4 = StrOption('val4', "", Calculation(calc_value, Params((ParamOption(val1), ParamOption(val2), ParamOption(val3)), join=ParamValue('.'), multi=ParamValue(True))), multi=True)
+    od = OptionDescription('root', '', [val1, val2, val3, val4])
+    async with await Config(od) as cfg:
+        cfg = await get_config(cfg, config_type)
+        assert await cfg.value.dict() == {'val1': ['val1'], 'val2': ['val2'], 'val3': [None], 'val4': []}
+        await cfg.option('val3').value.set(['val3'])
+        assert await cfg.value.dict() == {'val1': ['val1'], 'val2': ['val2'], 'val3': ['val3'], 'val4': ['val1.val2.val3']}
+    assert not await list_sessions()
+
+
 @pytest.mark.asyncio
 async def test_calc_value_min():
     val1 = StrOption('val1', "", 'val1')
diff --git a/tests/test_option_setting.py b/tests/test_option_setting.py
index 197168a..dbcabcf 100644
--- a/tests/test_option_setting.py
+++ b/tests/test_option_setting.py
@@ -768,6 +768,19 @@ async def test_set_modified_value():
     assert not await list_sessions()
 
 
+@pytest.mark.asyncio
+async def test_none_is_not_modified():
+    gcdummy = StrOption('dummy', 'dummy', properties=('force_store_value',))
+    gcdummy1 = StrOption('dummy1', 'dummy1', default="str", properties=('force_store_value',))
+    gcgroup = OptionDescription('gc', '', [gcdummy, gcdummy1])
+    descr = OptionDescription('tiramisu', '', [gcgroup])
+    async with await Config(descr) as cfg:
+        assert await cfg.value.exportation() == [[], [], [], []]
+        await cfg.property.read_write()
+        assert await cfg.value.exportation() == [['gc.dummy1'], [None], ['str'], ['forced']]
+    assert not await list_sessions()
+
+
 @pytest.mark.asyncio
 async def test_pprint():
     msg_error = _("cannot access to {0} \"{1}\" because has {2} {3}")
diff --git a/tiramisu/function.py b/tiramisu/function.py
index 447b186..8e2001e 100644
--- a/tiramisu/function.py
+++ b/tiramisu/function.py
@@ -347,14 +347,15 @@ class CalcValue:
                                 raise ValueError(_(f'unexpected value in calc_value with join attribute "{val}" with invalid length "{length_val}"'))
                             length_val = lval
                     new_value = []
-                    for idx in range(length_val):
-                        idx_val = []
-                        for val in value:
-                            if isinstance(val, list):
-                                idx_val.append(val[idx])
-                            else:
-                                idx_val.append(val)
-                        new_value.append(join.join(idx_val))
+                    if length_val is not None:
+                        for idx in range(length_val):
+                            idx_val = []
+                            for val in value:
+                                if isinstance(val, list):
+                                    idx_val.append(val[idx])
+                                else:
+                                    idx_val.append(val)
+                            new_value.append(join.join(idx_val))
                     value = new_value
                 else:
                     value = []
diff --git a/tiramisu/option/optiondescription.py b/tiramisu/option/optiondescription.py
index e9c90a6..3fd0806 100644
--- a/tiramisu/option/optiondescription.py
+++ b/tiramisu/option/optiondescription.py
@@ -132,9 +132,12 @@ class CacheOptionDescription(BaseOption):
                                               index,
                                               config_bag)
                         option_bag.properties = frozenset()
+                        value = await values.getvalue(option_bag)
+                        if value is None:
+                            continue
                         await values._p_.setvalue(config_bag.connection,
                                                   subpath,
-                                                  await values.getvalue(option_bag),
+                                                  value,
                                                   owners.forced,
                                                   index,
                                                   False)
@@ -163,9 +166,12 @@ class CacheOptionDescription(BaseOption):
                         option_bags.append(option_bag)
                     for option_bag in option_bags:
                         option_bag.properties = frozenset()
+                        value = await values.getvalue(option_bag)
+                        if value is None:
+                            continue
                         await values._p_.setvalue(config_bag.connection,
                                                   option_bag.path,
-                                                  await values.getvalue(option_bag),
+                                                  value,
                                                   owners.forced,
                                                   None,
                                                   False,