diff --git a/src/cal_tools/calcat_interface2.py b/src/cal_tools/calcat_interface2.py
index 0f5f58f90fef1e9f100923ee35e74b5f56f90db3..a23db25df3d283f79e61f644f57554e361ad55dd 100644
--- a/src/cal_tools/calcat_interface2.py
+++ b/src/cal_tools/calcat_interface2.py
@@ -68,6 +68,8 @@ class CalCatAPIClient:
             return dt.astimezone(timezone.utc).isoformat()
         elif isinstance(dt, date):
             return cls.format_time(datetime.combine(dt, time()))
+        elif dt is None:
+            return ""  # Not specified - for searches, this usually means now
         elif not isinstance(dt, str):
             raise TypeError(
                 f"Timestamp parameter ({dt!r}) must be a string, datetime or "