Why queryNorm is negative?

[Wei Zhao]

I got the debug info like this. It turns out that queryNorm is
negative so the total solr score is negative too. It is not really a
problem for me. But I'm curious why it can even be negative after
reading its definition (1/sumOfSquaredWeights)?


-1.1151254E-4 = (MATCH) product of:
  -0.0032338637 = (MATCH) sum of:
    -0.0032338637 = (MATCH) product of:
      -0.022637045 = (MATCH) sum of:
        -0.022637045 = (MATCH) weight(description_t:new in 171)
[DefaultSimilarity], result of:
          -0.022637045 = score(doc=171,freq=1.0), product of:
            -0.08188456 = queryWeight, product of:
              3.538569 = idf(docFreq=129, maxDocs=1646)
              -0.023140587 = queryNorm
            0.2764507 = fieldWeight in 171, product of:
              1.0 = tf(freq=1.0), with freq of:
                1.0 = termFreq=1.0
              3.538569 = idf(docFreq=129, maxDocs=1646)
              0.078125 = fieldNorm(doc=171)
      0.14285715 = coord(1/7)
  0.03448276 = coord(1/29)