parquet-hadoop/src/main/java/org/apache/parquet/hadoop/ParquetFileWriter.java
static MessageType mergeInto(MessageType toMerge, MessageType mergedSchema, boolean strict) {
    if (mergedSchema == null) {
      return toMerge;
    }

    return mergedSchema.union(toMerge, strict);
  }
static MessageType mergeInto(MessageType toMerge, MessageType mergedSchema, boolean strict) {
    if (mergedSchema == null) {
      return toMerge;
    }

    return mergedSchema.union(toMerge, strict);
  }
will return the result of merging toMerge into mergedSchema
@param toMerge the schema to merge into mergedSchema
@param mergedSchema the schema to append the fields to
@param strict should schema primitive types match
@return the resulting schema