**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:`

{
        
        if (!sample_columns)
            return false;
        if (sample_columns.columns() < 3)
            throw Exception{"Wrong arguments count", ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH};
        const auto * dict_name_col = checkAndGetColumnConst<ColumnString>(sample_columns.getByPosition(0).column.get());
        if (!dict_name_col)
            throw Exception{"First argument of function dictGet... must be a constant string", ErrorCodes::ILLEGAL_COLUMN};
        const auto * attr_name_col = checkAndGetColumnConst<ColumnString>(sample_columns.getByPosition(1).column.get());
        if (!attr_name_col)
            throw Exception{"Second argument of function dictGet... must be a constant string", ErrorCodes::ILLEGAL_COLUMN};
        return getDictionary(dict_name_col->getValue<String>())->isInjective(attr_name_col->getValue<String>());
    }
    DictionaryStructure getDictionaryStructure(const String & dictionary_name) const
    {
        return context.getExternalDictionariesLoader().getDictionaryStructure(dictionary_name, context);
    }
private:
    const Context & context;
    
    std::atomic<bool> access_checked = false;
    
    
    
    
    
};
class FunctionDictHas final : public IFunction