private static void initializeRegionMap() {
        REGION_MAP.clear();
        AWS_PARTITION = null;
        for (Partition partition : PARTITIONS) {
            if (partition.getId().equals("aws")) {
                AWS_PARTITION = partition;
            }
            for (String region : partition.getRegions().keySet()) {
                REGION_MAP.put(region, partition);
            }
        }
    }
Overrides the partitions provided by default. (changing this is not thread-safe).

@param partitions A list of partitions to set.
smithy-aws-endpoints/src/main/java/software/amazon/smithy/rulesengine/aws/language/functions/AwsPartition.java