refactor code to use defaults

Author: kai-ion

src/aws-cpp-sdk-core/source/endpoint/BuiltInParameters.cpp

@@ -42,6 +42,7 @@ namespace Endpoint
             static const char* FIPS_PREFIX = "fips-";
             static const char* FIPS_SUFFIX = "-fips";
             if (config.region.rfind(FIPS_PREFIX, 0) == 0) {
+                // Backward compatibility layer for code hacking previous SDK version
                 Aws::String regionOverride = config.region.substr(strlen(FIPS_PREFIX));
                 forceFIPS = true;
                 SetStringParameter(AWS_REGION, regionOverride);
@@ -62,12 +63,13 @@ namespace Endpoint
 
         if (!config.endpointOverride.empty()) {
             OverrideEndpoint(config.endpointOverride, config.scheme);
+
             if (config.region.empty()) {
                 AWS_LOGSTREAM_WARN(ENDPOINT_BUILTIN_LOG_TAG,
                                    "Endpoint is overridden but region is not set. "
                                    "Region is required by many endpoint rule sets to resolve the endpoint. "
                                    "And it is required to compute an aws signature.");
-                SetStringParameter(AWS_REGION, "region-not-set");
+                SetStringParameter(AWS_REGION, "region-not-set"); // dummy endpoint resolution parameter
             }
         } else if (!serviceName.empty()) {
             Aws::String resolvedEndpoint = Aws::Config::EndpointResolver::EndpointSource(serviceName, config.profileName);