#vulnerable code 
                                public File createDockerTarArchive(String imageName, MojoParameters params, BuildImageConfiguration buildConfig) throws MojoExecutionException {
        AssemblyConfiguration assemblyConfig = buildConfig.getAssemblyConfiguration();
        BuildDirs buildDirs = createBuildDirs(imageName, params);

        try {
            if (assemblyConfig != null &&
                (assemblyConfig.getInline() != null ||
                 assemblyConfig.getDescriptor() != null ||
                 assemblyConfig.getDescriptorRef() != null)) {
                createAssemblyArchive(assemblyConfig, params, buildDirs);
            }

            File extraDir = null;
            String dockerFileDir = assemblyConfig != null ? assemblyConfig.getDockerFileDir() : null;
            if (dockerFileDir != null) {
                // Use specified docker directory which must include a Dockerfile.
                extraDir = validateDockerDir(params, dockerFileDir);
            } else {
                // Create custom docker file in output dir
                DockerFileBuilder builder = createDockerFileBuilder(buildConfig, assemblyConfig);
                builder.write(buildDirs.getOutputDirectory());
            }
            return createTarball(buildDirs, extraDir, assemblyConfig.getMode());

        } catch (IOException e) {
            throw new MojoExecutionException(String.format("Cannot create Dockerfile in %s", buildDirs.getOutputDirectory()), e);
        }
    } 
                            #location 23 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public File createDockerTarArchive(String imageName, MojoParameters params, BuildImageConfiguration buildConfig) throws MojoExecutionException {
        BuildDirs buildDirs = createBuildDirs(imageName, params);
        
        AssemblyConfiguration assemblyConfig = buildConfig.getAssemblyConfiguration();
        AssemblyMode assemblyMode = (assemblyConfig == null) ? AssemblyMode.dir : assemblyConfig.getMode();

        if (hasAssemblyConfiguration(assemblyConfig)) {
            createAssemblyArchive(assemblyConfig, params, buildDirs);
        }
        
        try {
            File extraDir = null;
            String dockerFileDir = assemblyConfig != null ? assemblyConfig.getDockerFileDir() : null;
            if (dockerFileDir != null) {
                // Use specified docker directory which must include a Dockerfile.
                extraDir = validateDockerDir(params, dockerFileDir);
            } else {
                // Create custom docker file in output dir
                DockerFileBuilder builder = createDockerFileBuilder(buildConfig, assemblyConfig);
                builder.write(buildDirs.getOutputDirectory());
            }

            return createTarball(buildDirs, extraDir, assemblyMode);

        } catch (IOException e) {
            throw new MojoExecutionException(String.format("Cannot create Dockerfile in %s", buildDirs.getOutputDirectory()), e);
        }
    }