@Override
  public void copyToNewInstance(Object newInstance) throws UDFArgumentException {
    super.copyToNewInstance(newInstance); // Asserts the class invariant. (Same types.)
    GenericUDFInFile that = (GenericUDFInFile)newInstance;
    if (that != this) {
      that.set = (this.set == null ? null : (HashSet<String>)this.set.clone());
      that.strObjectInspector = this.strObjectInspector;
      that.fileObjectInspector = this.fileObjectInspector;
    }
  }
IN_FILE(str, filename) returns true if 'str' appears in the file specified
by 'filename'.  A string is considered to be in the file if it that string
appears as a line in the file.

If either argument is NULL then NULL is returned.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFInFile.java