only filter the result if there actually is a result and a filter

src/storm/cli/cli.cpp

@@ -683,7 +683,9 @@ namespace storm {
                                             } else {
                                                 filter = storm::api::verifyWithSparseEngine<ValueType>(sparseModel, storm::api::createTask<ValueType>(states, false));
                                             }
-                                            result->filter(filter->asQualitativeCheckResult());
+                                            if (result && filter) {
+                                                result->filter(filter->asQualitativeCheckResult());
+                                            }
                                             return result;
                                         });
         }
@@ -703,8 +705,9 @@ namespace storm {
                 } else {
                     filter = storm::api::verifyWithHybridEngine<DdType, ValueType>(symbolicModel, storm::api::createTask<ValueType>(states, false));
                 }
-                
-                result->filter(filter->asQualitativeCheckResult());
+                if (result && filter) {
+                    result->filter(filter->asQualitativeCheckResult());
+                }
                 return result;
             });
         }
@@ -724,8 +727,9 @@ namespace storm {
                 } else {
                     filter = storm::api::verifyWithDdEngine<DdType, ValueType>(symbolicModel, storm::api::createTask<ValueType>(states, false));
                 }
-                
-                result->filter(filter->asQualitativeCheckResult());
+                if (result && filter) {
+                    result->filter(filter->asQualitativeCheckResult());
+                }
                 return result;
             });
         }