How can I test the see if a file exists in the Inbox?

I am trying to test the existence of a file using the following code from a groovy blog:
File revFile = new File("test.csv")
println revFile.exists()
This file exists in the inbox/outbox.

When I validate the rule I receive the following message:
Error:The Groovy script failed to compile with internal error: Compile Error:
Expression [ConstructorCallExpression] is not allowed: new java.io.File(test.csv) Rule FPA.RPT.zFile_Exists
I assume this means I cannot create a file object. Since this is not an option does anyone have a method to verify the existence of a file in the inbox/outbox before running a process to load the file?