do not accept overwritting a node attribute with Null unless Null is the specified type

asyncua/server/address_space.py

@@ -725,9 +725,6 @@ class AddressSpace:
         return ua.StatusCode()
 
     def _is_expected_variant_type(self, value, attval, node):
-        if value.Value.VariantType == ua.VariantType.Null:
-            # we accept overwrite with Null, not sure if this is OK in spec...
-            return True
         vtype = attval.value.Value.VariantType
         if vtype == ua.VariantType.Null:
             # Node had a null value, many nodes are initialized with that value

examples/server-example.py

@@ -94,7 +94,8 @@ async def main():
     mydtvar = await myobj.add_variable(idx, "MyDateTimeVar", datetime.utcnow())
     await mydtvar.set_writable()    # Set MyVariable to be writable by clients
     myarrayvar = await myobj.add_variable(idx, "myarrayvar", [6.7, 7.9])
-    myarrayvar = await myobj.add_variable(idx, "myStronglytTypedVariable", ua.Variant([], ua.VariantType.UInt32))
+    await myobj.add_variable(idx, "myStronglytTypedVariable", ua.Variant([], ua.VariantType.UInt32))
+    await myarrayvar.set_writable(True)
     myprop = await myobj.add_property(idx, "myproperty", "I am a property")
     mymethod = await myobj.add_method(idx, "mymethod", func, [ua.VariantType.Int64], [ua.VariantType.Boolean])
     multiply_node = await myobj.add_method(idx, "multiply", multiply, [ua.VariantType.Int64, ua.VariantType.Int64], [ua.VariantType.Int64])

tests/test_common.py

@@ -439,7 +439,7 @@ async def test_utf8(opc):
 async def test_null_variable(opc):
     objects = opc.opc.nodes.objects
     var = await objects.add_variable(3, 'nullstring', "a string")
-    await var.write_value(None)
+    await var.write_value(ua.Variant(None, ua.VariantType.String))
     val = await var.read_value()
     assert val is None
     await var.write_value("")

tests/test_custom_structures.py

@@ -365,7 +365,7 @@ async def test_functional_advance(srv):
     await srv.srv.load_type_definitions()
 
     basic_var = await srv.srv.nodes.objects.add_variable(ua.NodeId(NamespaceIndex=srv.idx), 'BasicStruct',
-                                                    ua.Variant(None, ua.VariantType.Null),
+                                                    ua.Variant(None, ua.VariantType.ExtensionObject),
                                                     datatype=basic_struct.data_type)
 
     basic_msg = get_ua_class(basic_struct_name)()
@@ -375,7 +375,7 @@ async def test_functional_advance(srv):
     await basic_var.write_value(basic_msg)
 
     nested_var = await srv.srv.nodes.objects.add_variable(ua.NodeId(NamespaceIndex=srv.idx), 'NestedStruct',
-                                                     ua.Variant(None, ua.VariantType.Null),
+                                                     ua.Variant(None, ua.VariantType.ExtensionObject),
                                                      datatype=nested_struct.data_type)
 
     nested_msg = get_ua_class(nested_struct_name)()

tests/test_xml.py

@@ -228,7 +228,7 @@ async def test_xml_string(opc, tmpdir):
 
 async def test_xml_string_with_null_description(opc, tmpdir):
     o = await opc.opc.nodes.objects.add_variable(2, "xmlstring", "mystring")
-    await o.write_attribute(ua.AttributeIds.Description, ua.DataValue(None))
+    await o.write_attribute(ua.AttributeIds.Description, ua.DataValue(ua.Variant(ua.LocalizedText())))
     o2 = await _test_xml_var_type(opc, tmpdir, o, "string")
     assert await o.read_description() == await o2.read_description()
     await opc.opc.delete_nodes([o, o2])