BF: Handle missing description

ukbparse/main.py

@@ -17,6 +17,8 @@ import                        warnings
 import                        datetime
 import                        calendar
 
+import pandas              as pd
+
 import ukbparse
 import ukbparse.util       as util
 import ukbparse.icd10      as icd10
@@ -442,7 +444,7 @@ def generateDescription(dtable, col):
     vartable = dtable.vartable
     desc     = vartable.loc[col.vid, 'Description']
 
-    if desc == col.name:
+    if pd.isna(desc) or (desc == col.name):
         desc = 'n/a'
 
     # If metadata has been added to the column,