Reproduction steps:
```
CREATE TABLE table_left                                                                                                                                                                                              
(                                                                                                                                                                                                                    
    `date` Date,                                                                                                                                                                                                     
    `uid` String                                                                                                                                                                                                     
)                                                                                                                                                                                                                    
ENGINE = MergeTree()                                                                                                                                                                                                 
ORDER BY (date, uid)          
                                                                                                                                                                                       
CREATE TABLE table_right                                                                                                                                                                                             
(                                                                                                                                                                                                                    
    `date` Date,                                                                                                                                                                                                     
    `value` Decimal(18, 10)                                                                                                                                                                                          
)                                                                                                                                                                                                                    
ENGINE = MergeTree()                                                                                                                                                                                                 
ORDER BY date

INSERT INTO table_left values(toDate('2019-10-01'), 'hello');
INSERT INTO table_right values (toDate('2019-10-01'), 1), (toDate('2029-10-01'), 2);

SET join_use_nulls = 1;

SELECT ifNull(subquery_right.alias_value, 0)
FROM table_left
FULL OUTER JOIN 
(
    SELECT
        date,
        value AS alias_value
    FROM table_right
) AS subquery_right
ON table_left.date = subquery_right.date

Received exception from server (version 21.3.1):
Code: 43. DB::Exception: Received from localhost:9000. DB::Exception: Incompatible types of arguments corresponding to two conditional branches: while executing 'FUNCTION ifNull(alias_value :: 0, 0 :: 1) -> ifNull(alias_value, 0) Decimal(18, 10) : 2'. 
```
? else_is_nullable->getNullMapColumnPtr()
                        : DataTypeUInt8().createColumnConstWithDefaultValue(input_rows_count),
                    std::make_shared<DataTypeUInt8>(),
                    ""
                }
            });
            result_null_mask = executeImpl(temporary_columns, std::make_shared<DataTypeUInt8>(), input_rows_count);
        }
        ColumnPtr result_nested_column;
        {
            ColumnsWithTypeAndName temporary_columns(
            {
                arg_cond,
                {
                    recursiveGetNestedColumnWithoutNullable(arg_then.column),
                    removeNullable(arg_then.type),
                    ""
                },
                {
                    recursiveGetNestedColumnWithoutNullable(arg_else.column),
                    removeNullable(arg_else.type),
                    ""
                }
            });
            result_nested_column = executeImpl(temporary_columns, removeNullable(result_type), temporary_columns.front().column->size());
        }
        return ColumnNullable::create(
            materializeColumnIfConst(result_nested_column), materializeColumnIfConst(result_null_mask));
    }
    ColumnPtr executeForNullThenElse(const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, size_t input_rows_count) const