code: function addBannerToSourcemap (chunk, enc, next) {
        let pushed = false;
  
        if (banner) {
          // Get the sourcemap, once it exists
          let conv = convertSourcemap.fromSource(chunk.toString("utf8"));
          if (conv) {
            // Offset the sourcemap by the number of lines in the banner
            let offsetMap = offsetSourcemap(conv.toObject(), countLines(banner));
            this.push(new Buffer("\n" + convertSourcemap.fromObject(offsetMap).toComment() + "\n"));
            pushed = true;
          }
        }
  
        if (!pushed) {
          // This chunk doesn't contain anything for us to modify,
          // so just pass it along as-is
          this.push(chunk);
        }
        next();
      }
docs: Adjusts the sourcemap to account for the banner comment block