missing import

cgevans · cgevans · commit 06549ad637a0 · 2025-07-28T18:52:23.000+01:00
diff --git a/src/alhambra_mixes/references.py b/src/alhambra_mixes/references.py
@@ -18,6 +18,7 @@
     DecimalQuantity,
     _parse_conc_optional,
     _parse_conc_required,
+    NAN_CONC,
     nM,
     ureg,
 )
