21.2:

```
milovidov-desktop :) SELECT CAST(1111111111.222 AS DateTime64(3))

SELECT cast(1111111111.222, 'DateTime64(3)')

Query id: d10c8623-5c74-4a38-b535-a99f6af4d28d

┌─cast(1111111111.222, 'DateTime64(3)')─┐
│               2005-03-18 04:58:31.222 │
└───────────────────────────────────────┘
```

master:

```
milovidov-desktop :) SELECT CAST(1111111111.222 AS DateTime64(3))

SELECT cast(1111111111.222, 'DateTime64(3)')

Query id: cb4af967-a4ae-4df5-89ba-234d68675f93

┌─cast(1111111111.222, 'DateTime64(3)')─┐
│               2005-03-18 04:58:31.000 │
└───────────────────────────────────────┘
```
if (result_is_nullable)
        {
            return [wrapper, source_is_nullable]
                (ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, const ColumnNullable *, size_t input_rows_count) -> ColumnPtr
            {
                
                const auto & nullable_type = static_cast<const DataTypeNullable &>(*result_type);
                const auto & nested_type = nullable_type.getNestedType();
                ColumnsWithTypeAndName tmp_args;
                if (source_is_nullable)
                    tmp_args = createBlockWithNestedColumns(arguments);
                else
                    tmp_args = arguments;
                const ColumnNullable * nullable_source = nullptr;
                
                if (source_is_nullable)
                {
                    if (arguments.size() != 1)
                        throw Exception("Invalid number of arguments", ErrorCodes::LOGICAL_ERROR);
                    nullable_source = typeid_cast<const ColumnNullable *>(arguments.front().column.get());
                }
                
                auto tmp_res = wrapper(tmp_args, nested_type, nullable_source, input_rows_count);
                
                if (!tmp_res)
                    throw Exception("Couldn't convert " + arguments[0].type->getName() + " to "
                                    + nested_type->getName() + " in " + " prepareRemoveNullable wrapper.", ErrorCodes::LOGICAL_ERROR);
                return wrapInNullable(tmp_res, arguments, nested_type, input_rows_count);
            };
        }