Trap NaN frequencies and return None instead

data/spot.py

@@ -200,6 +200,10 @@ class Spot:
             if self.de_dxcc_id and not self.de_flag:
                 self.de_flag = lookup_helper.get_flag_for_dxcc(self.de_dxcc_id)
 
+        # Remove NaNs in frequency
+        if freq and freq == float("nan"):
+            freq = None
+
         # Band from frequency
         if self.freq and not self.band:
             band = infer_band_from_freq(self.freq)