I found that the Pvalue column is all -1 in the narrowpeak.bed file I downloaded from ENCODE. According to the manual provided by ENCODE, that means the Pvalues of all peaks are unassigned. Does anyone know what's the meaning of that? Thanks a lot.

Part of the peak file:

chrX    135117661       135118051       .       538     .       26.04842        -1      -1      195
chrX    107070120       107070510       .       538     .       26.06872        -1      -1      195
chr1    61139207        61139597        .       538     .       26.07643        -1      -1      195
chr17   62299372        62299762        .       539     .       26.09745        -1      -1      195