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 IColumn & col_from = *arguments[0].column;
        size_t size = col_from.size();
        const IDataType & data_type_to = *result_type;
        if (const ColumnString * col_from_string = checkAndGetColumn<ColumnString>(&col_from))
        {
            auto res = data_type_to.createColumn();
            IColumn & column_to = *res;
            column_to.reserve(size);
            const ColumnString::Chars & chars = col_from_string->getChars();
            const IColumn::Offsets & offsets = col_from_string->getOffsets();
            size_t current_offset = 0;
            FormatSettings format_settings;
            auto serialization = data_type_to.getDefaultSerialization();
            for (size_t i = 0; i < size; ++i)
            {
                ReadBufferFromMemory read_buffer(&chars[current_offset], offsets[i] - current_offset - 1);
                serialization->deserializeWholeText(column_to, read_buffer, format_settings);
                if (!read_buffer.eof())
                    throwExceptionForIncompletelyParsedValue(read_buffer, result_type);
                current_offset = offsets[i];
            }
            return res;
        }
        else
            throw Exception("Illegal column " + arguments[0].column->getName()
                    + " of first argument of conversion function from string",
                ErrorCodes::ILLEGAL_COLUMN);