Always reproduced:

```
milovidov-desktop :) create table table_map (a Map(String, String), b String) engine = MergeTree() order by a;

CREATE TABLE table_map
(
    `a` Map(String, String),
    `b` String
)
ENGINE = MergeTree
ORDER BY a

Query id: 8f8120c1-c165-452a-815f-2bcae3957e2a

Ok.

0 rows in set. Elapsed: 0.002 sec. 

milovidov-desktop :) SELECT b FROM table_map WHERE a = map('name', NULL, '', NULL)

SELECT b
FROM table_map
WHERE a = {'name', NULL, '', NULL}
```
{
        const auto & from_values = from_type->getValues();
        const auto & to_values = to_type->getValues();
        using ValueType = std::common_type_t<typename EnumTypeFrom::FieldType, typename EnumTypeTo::FieldType>;
        using NameValuePair = std::pair<std::string, ValueType>;
        using EnumValues = std::vector<NameValuePair>;
        EnumValues name_intersection;
        std::set_intersection(std::begin(from_values), std::end(from_values),
            std::begin(to_values), std::end(to_values), std::back_inserter(name_intersection),
            [] (auto && from, auto && to) { return from.first < to.first; });
        for (const auto & name_value : name_intersection)
        {
            const auto & old_value = name_value.second;
            const auto & new_value = to_type->getValue(name_value.first);
            if (old_value != new_value)
                throw Exception{"Enum conversion changes value for element '" + name_value.first +
                    "' from " + toString(old_value) + " to " + toString(new_value), ErrorCodes::CANNOT_CONVERT_TYPE};
        }
    }
    template <typename ColumnStringType, typename EnumType>
    WrapperType createStringToEnumWrapper() const