Problem about method Query#query()

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Hi all,

I pass some strings to org.apache.nutch.searcher.Query#parse() method,
but I got difference result like below:

parameter string: area:XX, returnedQuery.toString() is: area:XX.
parameter string: subarea:YY, returnedQuery.toString() is: subarea YY.
(Note: the ':' disappearred)
parameter string: publishdate:ZZ, returnedQuery.toString() is:
publishdate ZZ. (Note: the ':' disapperarred too)

So I can't query any content in field subarea & publishdate.

Why it is caused? Is it a bug or something I unknowed cuase it?

Thanks all.