Fix error in ctapipe-process in case telescope event is missing true …

…image

docs/changes/2659.bugfix.rst

@@ -0,0 +1,10 @@
+Fix error in ``ctapipe-process`` when in the middle of a simtel file
+that has true images available, a telescope event is missing the true image.
+This can happen rarely in case a telescope triggered on pure NSB or
+is oversaturated to the point where the true pe didn't fit into memory constraints.
+
+The error was due to the ``DataWriter`` trying to write a ``None`` into an
+already setup table for the true images.
+
+The ``SimTelEventSource`` will no create an invalid true image filled with ``-1``
+for such events.

src/ctapipe/io/simteleventsource.py

@@ -570,6 +570,7 @@ def __init__(self, input_url=Undefined, config=None, parent=None, **kwargs):
             self.file_, kind=self.atmosphere_profile_choice
         )
 
+        self._has_true_image = None
         self.log.debug(f"Using gain selector {self.gain_selector}")
 
     def __exit__(self, exc_type, exc_val, exc_tb):
@@ -872,6 +873,18 @@ def _generate_events(self):
                     .get("photoelectrons", None)
                 )
 
+                if self._has_true_image is None:
+                    self._has_true_image = true_image is not None
+
+                if self._has_true_image and true_image is None:
+                    self.log.warning(
+                        "Encountered telescope event with missing true_image in"
+                        "file that has true images: event_id = %d, tel_id = %d",
+                        event_id,
+                        tel_id,
+                    )
+                    true_image = np.full(n_pixels, -1, dtype=np.int32)
+
                 if data.simulation is not None:
                     if data.simulation.shower is not None:
                         impact_container = TelescopeImpactParameterContainer(