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'. 
```
const ColumnWithTypeAndName & arg_then = arguments[1];
        const ColumnWithTypeAndName & arg_else = arguments[2];
        
        if (arg_then.column.get() == arg_else.column.get())
        {
            
            return arg_then.column;
        }
        const ColumnUInt8 * cond_col = typeid_cast<const ColumnUInt8 *>(arg_cond.column.get());
        const ColumnConst * cond_const_col = checkAndGetColumnConst<ColumnVector<UInt8>>(arg_cond.column.get());
        ColumnPtr materialized_cond_col;
        if (cond_const_col)
        {
            if (arg_then.type->equals(*arg_else.type))
            {
                return cond_const_col->getValue<UInt8>()
                    ? arg_then.column
                    : arg_else.column;
            }
            else
            {
                materialized_cond_col = cond_const_col->convertToFullColumn();
                cond_col = typeid_cast<const ColumnUInt8 *>(&*materialized_cond_col);
            }
        }
        if (!cond_col)
            throw Exception("Illegal column " + arg_cond.column->getName() + " of first argument of function " + getName()
                + ". Must be ColumnUInt8 or ColumnConstUInt8.",
                ErrorCodes::ILLEGAL_COLUMN);
        auto call = [&](const auto & types) -> bool