private Map<String, SignerConfig> buildSignerMap(JsonIndex<SignerConfigJsonHelper, SignerConfig>[] signerIndexes,
                                                     String theme) {
        Map<String, SignerConfig> map = new HashMap<String, SignerConfig>();
        if (signerIndexes != null) {
            for (JsonIndex<SignerConfigJsonHelper, SignerConfig> index : signerIndexes) {
                String region = index.getKey();
                SignerConfig prev = map.put(region, index.newReadOnlyConfig());
                if (prev != null) {
                    log.warn("Duplicate definition of signer for " + theme + " " + index.getKey());
                }
            }
        }
        return map;
    }
Builds and returns a signer configuration map.

@param signerIndexes
           signer configuration entries loaded from JSON
@param theme
           used for message logging. eg region, service, region+service
aws-java-sdk-core/src/main/java/com/amazonaws/internal/config/InternalConfig.java