get inputStream from zipFile then add to another zipFile getting null pointer exception

Question

I'm trying to get input stream from zip file then add it to another zip file but it throws null pointer exception. here is my code.

       ZipParameters parameters = new ZipParameters();
       ZipFile newZipFile = new ZipFile(new File(CacheDir, "temp.card"));
       File temp = new File(CacheDir, "tempFile");
        if (!temp.exists()) {
                temp.createNewFile();
        }
       newZipFile.createZipFile(temp, parameters);
       if(newZipFile.getFile().exist()){
       if (string != null) {
            inputStream = zipFile.getInputStream(zipFile.getFileHeader(string));
       }
       if (inputStream != null) {
            newZipFile.addStream(inputStream,parameters);
       }
       }

non of objects in this scope are null. but I'm getting exception here:

newZipFile.addStream(inputStream,parameters);

Log:

12-14 06:27:43.891: W/System.err(2197): net.lingala.zip4j.exception.ZipException: input file is null
12-14 06:27:43.891: W/System.err(2197):     at net.lingala.zip4j.io.CipherOutputStream.putNextEntry(CipherOutputStream.java:71)
12-14 06:27:43.895: W/System.err(2197):     at net.lingala.zip4j.io.DeflaterOutputStream.putNextEntry(DeflaterOutputStream.java:45)
12-14 06:27:43.895: W/System.err(2197):     at net.lingala.zip4j.zip.ZipEngine.addStreamToZip(ZipEngine.java:230)
12-14 06:27:43.895: W/System.err(2197):     at net.lingala.zip4j.core.ZipFile.addStream(ZipFile.java:395)

Answer 1

Tracing that exception to its origin, I found in the source code of zip4j that

if (!zipParameters.isSourceExternalStream() && file == null) {
    throw new ZipException("input file is null");
}

So the quick fix is to bypass that check by

parameters.setSourceExternalStream(true);

P.S.: I have no idea what externalStream means, but it worked