check for snap reference layer before starting layer alignment

src/cplus_plugin/gui/qgis_cplus_main.py

@@ -1228,7 +1228,13 @@ def pathways_analysis_done(
             snapping_enabled = settings_manager.get_value(
                 Settings.SNAPPING_ENABLED, default=False, setting_type=bool
             )
-            if snapping_enabled:
+            reference_layer = settings_manager.get_value(Settings.SNAP_LAYER)
+            reference_layer_path = Path(reference_layer)
+            if (
+                snapping_enabled
+                and os.path.exists(reference_layer)
+                and reference_layer_path.is_file()
+            ):
                 self.snap_analyzed_pathways(
                     pathways, models, priority_layers_groups, extent
                 )
@@ -1999,7 +2005,13 @@ def run_priority_analysis(self, models, priority_layers_groups, extent):
             settings_model = settings_manager.get_implementation_model(str(model.uuid))
 
             for layer in settings_model.priority_layers:
+                if layer is None:
+                    continue
+
                 settings_layer = settings_manager.get_priority_layer(layer.get("uuid"))
+                if settings_layer is None:
+                    continue
+
                 pwl = settings_layer.get("path")
 
                 missing_pwl_message = (

src/cplus_plugin/utils.py

@@ -316,7 +316,10 @@ def align_rasters(
             )
             raise Exception(align.errorMessage())
     except Exception as e:
-        log(f"Problem occured when snapping, {str(e)}")
+        log(
+            f"Problem occured when snapping, {str(e)}."
+            f" Update snap settings and re-run the analysis"
+        )
 
     log(
         f"Finished snapping using resampling method {resample_method_value.name} with"