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)
```
else
                return nullptr;
            return col_res_untyped;
        }
        if (isString(result_type))
        {
            
            auto col_res = ColumnString::create();
            auto sink = StringSink(*col_res, rows);
            if (col_then && col_else)
                conditional(StringSource(*col_then), StringSource(*col_else), sink, cond_data);
            else if (col_then && col_else_const)
                conditional(StringSource(*col_then), ConstSource<StringSource>(*col_else_const), sink, cond_data);
            else if (col_then_const && col_else)
                conditional(ConstSource<StringSource>(*col_then_const), StringSource(*col_else), sink, cond_data);
            else if (col_then_const && col_else_const)
                conditional(ConstSource<StringSource>(*col_then_const), ConstSource<StringSource>(*col_else_const), sink, cond_data);
            else if (col_then && col_else_fixed)
                conditional(StringSource(*col_then), FixedStringSource(*col_else_fixed), sink, cond_data);
            else if (col_then_fixed && col_else)
                conditional(FixedStringSource(*col_then_fixed), StringSource(*col_else), sink, cond_data);
            else if (col_then_const && col_else_fixed)
                conditional(ConstSource<StringSource>(*col_then_const), FixedStringSource(*col_else_fixed), sink, cond_data);
            else if (col_then_fixed && col_else_const)
                conditional(FixedStringSource(*col_then_fixed), ConstSource<StringSource>(*col_else_const), sink, cond_data);
            else if (col_then && col_else_const_fixed)
                conditional(StringSource(*col_then), ConstSource<FixedStringSource>(*col_else_const_fixed), sink, cond_data);
            else if (col_then_const_fixed && col_else)
                conditional(ConstSource<FixedStringSource>(*col_then_const_fixed), StringSource(*col_else), sink, cond_data);
            else if (col_then_const && col_else_const_fixed)