For example, if I use UInt8 constant for if condition then only one branch is evaluated:
```sql
SELECT if(1, 'success', throwIf(1, 'Executing FALSE branch'))

┌─'success'─┐
│ success   │
└───────────┘

1 rows in set. Elapsed: 0.003 sec.
```

But if I use some constant expression, then both branches are evaluated:
```sql
SELECT if(empty(''), 'success', throwIf(1, 'Executing FALSE branch'))

0 rows in set. Elapsed: 0.003 sec.

Received exception from server (version 21.12.2):
Code: 395. DB::Exception: Received from localhost:9000. DB::Exception: Executing FALSE branch: While processing if(empty(''), 'success', throwIf(1, 'Executing FALSE branch')). (FUNCTION_THROW_IF_VALUE_IS_NON_ZERO)
```
conditional(ConstSource<StringSource>(*col_then_const), ConstSource<FixedStringSource>(*col_else_const_fixed), sink, cond_data);
            else if (col_then_const_fixed && col_else_const)
                conditional(ConstSource<FixedStringSource>(*col_then_const_fixed), ConstSource<StringSource>(*col_else_const), sink, cond_data);
            else if (col_then_fixed && col_else_fixed)
                conditional(FixedStringSource(*col_then_fixed), FixedStringSource(*col_else_fixed), sink, cond_data);
            else if (col_then_fixed && col_else_const_fixed)
                conditional(FixedStringSource(*col_then_fixed), ConstSource<FixedStringSource>(*col_else_const_fixed), sink, cond_data);
            else if (col_then_const_fixed && col_else_fixed)
                conditional(ConstSource<FixedStringSource>(*col_then_const_fixed), FixedStringSource(*col_else_fixed), sink, cond_data);
            else if (col_then_const_fixed && col_else_const_fixed)
                conditional(ConstSource<FixedStringSource>(*col_then_const_fixed),
                            ConstSource<FixedStringSource>(*col_else_const_fixed), sink, cond_data);
            else
                return nullptr;
            return col_res;
        }
        return nullptr;
    }
    static ColumnPtr executeGenericArray(const ColumnUInt8 * cond_col, const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type)
    {
        
        if (!arguments[1].type->equals(*arguments[2].type))
            return nullptr;
        const IColumn * col_then_untyped = arguments[1].column.get();
        const IColumn * col_else_untyped = arguments[2].column.get();
        const ColumnArray * col_arr_then = checkAndGetColumn<ColumnArray>(col_then_untyped);
        const ColumnArray * col_arr_else = checkAndGetColumn<ColumnArray>(col_else_untyped);
        const ColumnConst * col_arr_then_const = checkAndGetColumnConst<ColumnArray>(col_then_untyped);
        const ColumnConst * col_arr_else_const = checkAndGetColumnConst<ColumnArray>(col_else_untyped);
        const PaddedPODArray<UInt8> & cond_data = cond_col->getData();