[...]
def files = new File('.').eachFile(FileType.FILES)
		for(String file: files){
			echo file
		}
[...]

new java.io.File java.lang.String
staticField groovy.io.FileType FILES

org.jenkinsci.plugins.scriptsecurity.sandbox.RejectedAccessException: unclassified method java.io.File eachFileRecurse groovy.io.FileType
	at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onMethodCall(SandboxInterceptor.java:113)
	at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:149)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:146)
	at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.methodCall(SandboxInvoker.java:16)
	at WorkflowScript.run(WorkflowScript:22)
	at ___cps.transform___(Native Method)
	at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:57)
	at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:109)
	at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:82)
	at sun.reflect.GeneratedMethodAccessor311.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
	at com.cloudbees.groovy.cps.impl.PropertyishBlock$ContinuationImpl.get(PropertyishBlock.java:76)
	at com.cloudbees.groovy.cps.LValueBlock$GetAdapter.receive(LValueBlock.java:30)
	at com.cloudbees.groovy.cps.impl.PropertyishBlock$ContinuationImpl.fixName(PropertyishBlock.java:66)
	at sun.reflect.GeneratedMethodAccessor347.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
	at com.cloudbees.groovy.cps.impl.ConstantBlock.eval(ConstantBlock.java:21)
	at com.cloudbees.groovy.cps.Next.step(Next.java:58)
	at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:154)
	at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:18)
	at org.jenkinsci.plugins.workflow.cps.SandboxContinuable$1.call(SandboxContinuable.java:33)
	at org.jenkinsci.plugins.workflow.cps.SandboxContinuable$1.call(SandboxContinuable.java:30)
	at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.GroovySandbox.runInSandbox(GroovySandbox.java:108)
	at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:30)
	at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:163)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:324)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$100(CpsThreadGroup.java:78)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:236)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:224)
	at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:63)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:112)
	at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)