Check Null

CallReport.java

import java.io.File;

public class CallReport {

    public static void main(String ... args) {

        Report report = new NotNullReport(new FileNotExistsReport(new DefaultReport()));
        report.export(null);  //Throw error from null
        report.export(new File("existing.pdf")); //Throw error from existing file
        report.export(new File("new.pdf")); //Success
    }

}

NewReport.java

import java.io.File;

public interface Report {
    void export(File file);
}

class DefaultReport implements Report {

    @Override
    public void export(File file) {

    }
}

class FileNotExistsReport implements Report {

    private final Report originalReport;

    public FileNotExistsReport(Report report) {
        this.originalReport = report;
    }

    @Override
    public void export(File file) {
        if(file.exists()) {
            throw new IllegalArgumentException( "File already exists." );
        }
        System.out.println(file.getAbsoluteFile());
        this.originalReport.export(file);
    }
}

class NotNullReport extends FileNotExistsReport {

    private final Report originalReport;

    public NotNullReport(Report report) {
        super(report);
        this.originalReport = report;
    }

    @Override
    public void export(File file) {
        if(file == null) {
            throw new IllegalArgumentException( "File is NULL; can't export." );
        }
        this.originalReport.export(file);
    }
}

Report.java

import java.io.File;

class Report {
    void export(File file) {
        if (file == null) {
            throw new IllegalArgumentException( "File is NULL; can't export." );
        }
        if (file.exists()) {
            throw new IllegalArgumentException( "File already exists." );
        }
    }
}