When the Unified Agent identifies a package.json file, it tries to determine whether it is an NPM or a yarn project based on the relevant lock file. If a yarn.lock is identified, then the yarn resolution is performed, otherwise, if package-lock.json is identified NPM resolution is performed. Only in the case in which both lock files are found, the Unified Agent will use the npm.yarnProject parameter to determine which resolution to perform.
For more information, see the Unified Agent Configuration Parameters page.