#vulnerable code 
                                @Override
    public void execute() throws MojoExecutionException, MojoFailureException {
        try {
            // set git flow configuration
            initGitFlowConfig();

            // check uncommitted changes
            checkUncommittedChanges();

            // check snapshots dependencies
            if (!allowSnapshots) {
                checkSnapshotDependencies();
            }

            // git for-each-ref --count=1 refs/heads/release/*
            final String releaseBranch = gitFindBranches(
                    gitFlowConfig.getReleaseBranchPrefix(), true);

            if (StringUtils.isNotBlank(releaseBranch)) {
                throw new MojoFailureException(
                        "Release branch already exists. Cannot start release.");
            }

            // fetch and check remote
            if (fetchRemote) {
                gitFetchRemoteAndCompare(gitFlowConfig.getDevelopmentBranch());
            }

            // need to be in develop to get correct project version
            // git checkout develop
            gitCheckout(gitFlowConfig.getDevelopmentBranch());

            // get current project version from pom
            final String currentVersion = getCurrentProjectVersion();

            String defaultVersion = null;
            if (tychoBuild) {
                defaultVersion = currentVersion;
            } else {
                // get default release version
                try {
                    final DefaultVersionInfo versionInfo = new DefaultVersionInfo(
                            currentVersion);
                    defaultVersion = versionInfo.getReleaseVersionString();
                } catch (VersionParseException e) {
                    if (getLog().isDebugEnabled()) {
                        getLog().debug(e);
                    }
                }
            }

            if (defaultVersion == null) {
                throw new MojoFailureException(
                        "Cannot get default project version.");
            }

            String version = null;
            if (settings.isInteractiveMode()) {
                try {
                    version = prompter.prompt("What is release version? ["
                            + defaultVersion + "]");
                } catch (PrompterException e) {
                    getLog().error(e);
                }
            }

            if (StringUtils.isBlank(version)) {
                version = defaultVersion;
            }

            String branchName = gitFlowConfig.getReleaseBranchPrefix();
            if (!sameBranchName) {
                branchName += version;
            }

            // git checkout -b release/... develop
            gitCreateAndCheckout(branchName,
                    gitFlowConfig.getDevelopmentBranch());

            // execute if version changed
            if (!version.equals(currentVersion)) {
                // mvn versions:set -DnewVersion=... -DgenerateBackupPoms=false
                mvnSetVersions(version);

                // git commit -a -m updating versions for release
                gitCommit(commitMessages.getReleaseStartMessage());
            }

            if (installProject) {
                // mvn clean install
                mvnCleanInstall();
            }
        } catch (CommandLineException e) {
            getLog().error(e);
        }
    } 
                            #location 81 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public void execute() throws MojoExecutionException, MojoFailureException {
        try {
            // set git flow configuration
            initGitFlowConfig();

            // check uncommitted changes
            checkUncommittedChanges();

            // check snapshots dependencies
            if (!allowSnapshots) {
                checkSnapshotDependencies();
            }

            // git for-each-ref --count=1 refs/heads/release/*
            final String releaseBranch = gitFindBranches(
                    gitFlowConfig.getReleaseBranchPrefix(), true);

            if (StringUtils.isNotBlank(releaseBranch)) {
                throw new MojoFailureException(
                        "Release branch already exists. Cannot start release.");
            }

            // fetch and check remote
            if (fetchRemote) {
                gitFetchRemoteAndCompare(gitFlowConfig.getDevelopmentBranch());
            }

            // need to be in develop to get correct project version
            // git checkout develop
            gitCheckout(gitFlowConfig.getDevelopmentBranch());

            // get current project version from pom
            final String currentVersion = getCurrentProjectVersion();

            String defaultVersion = null;
            if (tychoBuild) {
                defaultVersion = currentVersion;
            } else {
                // get default release version
                try {
                    final DefaultVersionInfo versionInfo = new DefaultVersionInfo(
                            currentVersion);
                    defaultVersion = versionInfo.getReleaseVersionString();
                } catch (VersionParseException e) {
                    if (getLog().isDebugEnabled()) {
                        getLog().debug(e);
                    }
                }
            }

            if (defaultVersion == null) {
                throw new MojoFailureException(
                        "Cannot get default project version.");
            }

            String version = null;
            if (settings.isInteractiveMode()) {
                try {
                    version = prompter.prompt("What is release version? ["
                            + defaultVersion + "]");
                } catch (PrompterException e) {
                    getLog().error(e);
                }
            } else {
                version = releaseVersion;
            }

            if (StringUtils.isBlank(version)) {
                version = defaultVersion;
            }

            String branchName = gitFlowConfig.getReleaseBranchPrefix();
            if (!sameBranchName) {
                branchName += version;
            }

            // git checkout -b release/... develop
            gitCreateAndCheckout(branchName,
                    gitFlowConfig.getDevelopmentBranch());

            // execute if version changed
            if (!version.equals(currentVersion)) {
                // mvn versions:set -DnewVersion=... -DgenerateBackupPoms=false
                mvnSetVersions(version);

                // git commit -a -m updating versions for release
                gitCommit(commitMessages.getReleaseStartMessage());
            }

            if (installProject) {
                // mvn clean install
                mvnCleanInstall();
            }
        } catch (CommandLineException e) {
            getLog().error(e);
        }
    }