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_low_cardinality = typeid_cast<const DataTypeLowCardinality *>(from_type.get());
        const auto * to_low_cardinality = typeid_cast<const DataTypeLowCardinality *>(to_type.get());
        const auto & from_nested = from_low_cardinality ? from_low_cardinality->getDictionaryType() : from_type;
        const auto & to_nested = to_low_cardinality ? to_low_cardinality->getDictionaryType() : to_type;
        if (from_type->onlyNull())
        {
            if (!to_nested->isNullable())
            {
                if (cast_type == CastType::accurateOrNull)
                {
                    return createToNullableColumnWrapper();
                }
                else
                {
                    throw Exception{"Cannot convert NULL to a non-nullable type", ErrorCodes::CANNOT_CONVERT_TYPE};
                }
            }
            return [](ColumnsWithTypeAndName &, const DataTypePtr & result_type, const ColumnNullable *, size_t input_rows_count)
            {
                return result_type->createColumnConstWithDefaultValue(input_rows_count)->convertToFullColumnIfConst();
            };
        }
        bool skip_not_null_check = false;
        if (from_low_cardinality && from_nested->isNullable() && !to_nested->isNullable())
            
            skip_not_null_check = true;