How to remove metadata "Keywords" information?

I can remove metadata "Title", "Author", "Subject" successfully by codes below:
 
this.info.title = "";
this.info.author = "";
this.info.subject = "";
 
But when I try to move metadata "Keywords", the following code doesn't work:
 
this.info.keywords = "";
 
It will add a semicolon before the original information, e.g. the original "Keywords" field is "abcdefg", after running the following code, it changes to ";abcdefg":
  
could you kindly advise how to remove all "Keywords" information by JavaScript? Thanks a lot!
 
PS: I know this can be realized by Batch Processing of Acrobat, but I need to do this by JavaScript. :(