Odd, finding a "NULNULL" value in 2001 csv

[adamrossnelson]

I'm looking at the 2001 csv (MERGED2001_02_PP.csv) and finding at least one instance of a value "NULNULL." Fishing this out in Stata...

. tab ret_ftl4_pooled

RET_FTL4_PO |
       OLED |      Freq.     Percent        Cum.
------------+-----------------------------------
         .n |      6,618       99.98       99.98
    NULNULL |          1        0.02      100.00
------------+-----------------------------------
      Total |      6,619      100.00

. list ïunitid instnm ret_ftl4_pooled if ret_ftl4_pooled == "NULNULL"

      +---------------------------------------------------+
      | ïunitid                         instnm   ret_ft.. |
      |---------------------------------------------------|
3968. |  217581   Empire Beauty School-Warwick    NULNULL |
      +---------------------------------------------------+

Edit:
This observation, in this year only, has at least one other unusual value poolyrsret_pt seems to be "L"