**Describe the unexpected behaviour**
If Null being passed as dictionary key, dictGetOrDefault returns null instead of default value.

**How to reproduce**
Clickhouse version 21.5, 21.1, 20.8

```

CREATE VIEW dict_null_source AS SELECT 1 as key, 1 as val;
CREATE DICTIONARY dict_null (key UInt64, val UInt32) PRIMARY KEY key SOURCE(CLICKHOUSE(host 'localhost' user 'default' table 'dict_null_source' ))LAYOUT(FLAT)LIFETIME(300)


SELECT dictGetOrDefault('default.dict_null', 'val', CAST(NULL, 'Nullable(UInt64)'), 0) AS val

Query id: 79518a8e-b439-4d08-a0b2-85e4b3ef99eb

┌──val─┐
│ ᴺᵁᴸᴸ │
└──────┘
```

**Additional context**
```

SELECT dictGetOrDefault('default.dict_null', 'val', CAST(1, 'UInt64'))

Query id: 71ec76a1-fb61-4641-9145-79c6bfffd490


0 rows in set. Elapsed: 0.001 sec.

Received exception from server (version 21.5.1):
Code: 42. DB::Exception: Received from localhost:9000. DB::Exception: Wrong argument count for function dictGetOrDefault: While processing dictGetOrDefault('default.dict_null', 'val', CAST(1, 'UInt64')).

```

Error message in 21.1 was better:  `Number of arguments for function dictGetOrDefault doesn't match: passed 3, should be 4:`

attribute_names.emplace_back(name_col->getValue<String>());
        else if (const auto * tuple_col_const = checkAndGetColumnConst<ColumnTuple>(column.get()))
        {
            const ColumnTuple & tuple_col = assert_cast<const ColumnTuple &>(tuple_col_const->getDataColumn());
            size_t tuple_size = tuple_col.tupleSize();
            if (tuple_size < 1)
                throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT,
                    "Tuple second argument of function ({}) must contain multiple constant string columns");
            for (size_t i = 0; i < tuple_col.tupleSize(); ++i)
            {
                const auto * tuple_column = tuple_col.getColumnPtr(i).get();
                const auto * attribute_name_column = checkAndGetColumn<ColumnString>(tuple_column);
                if (!attribute_name_column)
                    throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT,
                        "Tuple second argument of function ({}) must contain multiple constant string columns",
                        getName());
                attribute_names.emplace_back(attribute_name_column->getDataAt(0));
            }
        }
        else
            throw Exception(ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT,
                "Illegal type ({}) of second argument of function ({}), expected a const string or const tuple of const strings.",
                type->getName(),
                getName());
        return attribute_names;
    }
    mutable FunctionDictHelper helper;
};
template <typename DataType, typename Name, DictionaryGetFunctionType dictionary_get_function_type>
class FunctionDictGetImpl final : public IFunction