Error msg no writecb in Transform class when tried to add sourcemaps support.

[hzlzh]

Error msg no writecb in Transform class when tried to add sourcemaps support.
How to solve this?

if (obj.stylesheet.rules.length > 0) {
            parseRules(obj.stylesheet.rules);
            cssContent = css.stringify(obj, { sourcemap: true });
        }

        if (file.sourceMap) {
            applySourceMap(file, cssContent.map);
        }

        this.push(new File({
            base: file.base,
            path: file.path,
            contents: new Buffer(cssContent.code)
        }));

        cb();

issues here weixin/gulp-lazyimagecss#1

[phated]

This is a problem with your usage of streams, not anything to do with gulp-sourcemaps.