Replace nested Stream.concat with direct iteration in expression merging#6725

RanVaknin wants to merge 4 commits intomasteraws/aws-sdk-java-v2:masterfrom

rvaknin/ddb-optimization-updateExpression-stream-flatteningaws/aws-sdk-java-v2:rvaknin/ddb-optimization-updateExpression-stream-flatteningCopy head branch name to clipboard