[I] [C++][Parquet] MinMax statistics for strings may be inaccurate after a merge [arrow]

["rip-nsk (via GitHub)" <gi...@apache.org>]

rip-nsk opened a new issue, #47995:
URL: https://github.com/apache/arrow/issues/47995

   ### Describe the bug, including details regarding any error messages, version, and platform.
   
   TypedStatistics::Megre function disregards column chunks when the minimum value is an empty string (represented as {null, 0}) due to the following code:
   ```c++
   optional<std::pair<ByteArray, ByteArray>> CleanStatistic(
       std::pair<ByteArray, ByteArray> min_max, LogicalType::Type::type) {
     if (min_max.first.ptr == nullptr || min_max.second.ptr == nullptr) {
       return ::std::nullopt;
     }
     return min_max;
   }
   ```
   so both minimum and maximum values will be lost.
   
   ### Component(s)
   
   C++


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