20.7
```
SELECT indexOf(['a', 'b', 'c'], toLowCardinality('a'))

┌─indexOf(['a', 'b', 'c'], toLowCardinality('a'))─┐
│                                               1 │
└─────────────────────────────────────────────────┘
```

20.8
```
SELECT indexOf(['a', 'b', 'c'], toLowCardinality('a'))


Received exception from server (version 20.8.3):
Code: 43. DB::Exception: Received from localhost:9000. DB::Exception: Types of array and 2nd argument of function "indexOf" must be identical up to nullability, cardinality, numeric types, or Enum and numeric type. Passed: Array(String) and LowCardinality(String).. 
```

https://github.com/ClickHouse/ClickHouse/pull/12550

/cc @myrrc 

{
        if (allowNested(array_inner_type, arg))
            return true;
        
        const bool array_is_nullable = array_inner_type->isNullable();
        const bool arg_is_nullable = arg->isNullable();
        const DataTypePtr arg_or_arg_nullable_nested = arg_is_nullable
            ? checkAndGetDataType<DataTypeNullable>(arg.get())->getNestedType()
            : arg;
        if (array_is_nullable) 
        {
            const DataTypePtr array_nullable_nested =
                checkAndGetDataType<DataTypeNullable>(array_inner_type.get())->getNestedType();
            return allowNested(
                    array_nullable_nested,
                    arg_or_arg_nullable_nested);
        }
        else if (arg_is_nullable) 
            return false;
        
        const auto * const array_lc_ptr = checkAndGetDataType<DataTypeLowCardinality>(array_inner_type.get());
        const auto * const arg_lc_ptr = checkAndGetDataType<DataTypeLowCardinality>(arg.get());
        const DataTypePtr array_lc_inner_type = recursiveRemoveLowCardinality(array_inner_type);
        const DataTypePtr arg_lc_inner_type = recursiveRemoveLowCardinality(arg);
        const bool array_is_lc = nullptr != array_lc_ptr;
        const bool arg_is_lc = nullptr != arg_lc_ptr;
        const bool array_lc_inner_type_is_nullable = array_is_lc && array_lc_inner_type->isNullable();