1 files changed, 10 insertions, 11 deletions

diff --git a/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java b/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java
index 84af4ee6..0d35fb03 100644
--- a/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java
+++ b/subprojects/language/src/main/java/tools/refinery/language/validation/ProblemValidator.java
@@ -520,18 +520,17 @@ public class ProblemValidator extends AbstractProblemValidator {
 
         @Nullable
         private Node getNodeArgumentForMultiObjectAssertion(AssertionArgument argument) {
-                if (argument instanceof WildcardAssertionArgument) {
-                        acceptError("Wildcard arguments for 'exists' are not supported.", argument, null, 0,
-                                        UNSUPPORTED_ASSERTION_ISSUE);
-                        return null;
-                }
-                if (argument instanceof NodeAssertionArgument nodeAssertionArgument) {
-                        var variableOrNode = nodeAssertionArgument.getNode();
-                        if (variableOrNode == null || variableOrNode instanceof Node) {
-                                return (Node) variableOrNode;
+                return switch (argument) {
+                        case null -> null;
+                        case WildcardAssertionArgument ignoredWildcardAssertionArgument -> {
+                                acceptError("Wildcard arguments for 'exists' are not supported.", argument, null, 0,
+                                                UNSUPPORTED_ASSERTION_ISSUE);
+                                yield null;
                         }
-                }
-                throw new IllegalArgumentException("Unknown assertion argument: " + argument);
+                        case NodeAssertionArgument nodeAssertionArgument ->
+                                        nodeAssertionArgument.getNode() instanceof Node node ? node : null;
+                        default -> throw new IllegalArgumentException("Unknown assertion argument: " + argument);
+                };
         }
 
         @Check