gulp sass with sourcemap

gistfile1.js

gulp.task('sass', function() {
  gulp.src(['assets/scss/**/*.scss', '!assets/scss/templates/*.scss'])
    .pipe(plumber({errorHandler: on_Error}))
    .pipe(gulpif(condition, sass({require: ['susy'], style: 'expanded', sourcemap: true}), sass()))
    .pipe(filter('**/*.css'))
    .pipe(sourcemaps.init({loadMaps:true}))
    .pipe(postcss([autoprefixer({ browsers: ['last 2 version', 'ie 9'], cascade: true})]))
    .on('error', function(err) { console.log(err.message); })
    .pipe(sourcemaps.write('.'))
    .pipe(gulp.dest('dist/css'))
    .pipe(filter('**/*.css'))
    .pipe(notify("compiled SCSS"))
    .pipe(browserSync.reload({stream: true}));
});