When attempting to run the expression new String(java.nio.file.Files.readAllBytes(java.nio.file.Paths.get("/some/path"))) in a sandboxed pipeline script, I get the following error:

org.jenkinsci.plugins.scriptsecurity.sandbox.RejectedAccessException: unclassified staticMethod java.nio.file.Paths get java.lang.String

Also, no approval appears at /scriptApproval.