Reproduce the reported issue

CHANGELOG.md

@@ -13,6 +13,7 @@ Currently the versioning policy of this project follows [Semantic Versioning v2.
 - Fixed traversal of nested archives governed by `-nested:true` ([#1930](https://github.com/spotbugs/spotbugs/pull/1930))
 - Warnings of deprecated System::setSecurityManager calls on Java 17 ([#1983](https://github.com/spotbugs/spotbugs/pull/1983))
 - Fixed false positive SSD bug for locking on java.lang.Class objects ([#1978](https://github.com/spotbugs/spotbugs/issues/1978))
+- FindReturnRef throws an IllegalArgumentException unexpectedly ([#2019](https://github.com/spotbugs/spotbugs/issues/2019))
 - Bump ObjectWeb ASM from 9.2 to 9.3 supporting JDK 19 ([#2004](https://github.com/spotbugs/spotbugs/pull/2004))
 
 ### Added

spotbugs-tests/src/test/java/edu/umd/cs/findbugs/detect/Issue2019Test.java

@@ -0,0 +1,17 @@
+package edu.umd.cs.findbugs.detect;
+
+import edu.umd.cs.findbugs.AbstractIntegrationTest;
+import org.junit.Test;
+
+
+public class Issue2019Test extends AbstractIntegrationTest {
+    @Test
+    public void test() {
+        performAnalysis("ghIssues/Issue2019$ATNSimulator.class",
+                "ghIssues/Issue2019$BaseParser.class",
+                "ghIssues/Issue2019$Parser.class",
+                "ghIssues/Issue2019$ParserATNSimulator.class",
+                "ghIssues/Issue2019$Recognizer.class",
+                "ghIssues/Issue2019.class");
+    }
+}

spotbugs/src/main/java/edu/umd/cs/findbugs/detect/FindReturnRef.java

@@ -296,7 +296,7 @@ public void afterOpcode(int seen) {
             }
         }
 
-        if (seen == Const.CHECKCAST) {
+        if (seen == Const.CHECKCAST && !stack.isTop()) {
             OpcodeStack.Item item = stack.getStackItem(0);
             if (fieldCloneUnderCast != null) {
                 arrayFieldClones.put(item, fieldCloneUnderCast);

spotbugsTestCases/src/java/ghIssues/Issue2019.java

@@ -0,0 +1,44 @@
+package ghIssues;
+
+/**
+ * @see <a href="https://github.com/spotbugs/spotbugs/issues/2019">GitHub Issue</a>
+ */
+public class Issue2019 {
+
+    static class ATNSimulator {
+        public int adaptivePredict() {
+            return 0;
+        }
+    }
+
+    static class ParserATNSimulator extends ATNSimulator {
+    }
+
+    static class Recognizer<ATNInterpreter extends ATNSimulator> {
+        public ATNInterpreter getInterpreter() {
+            return null;
+        }
+    }
+
+    static class BaseParser extends Recognizer<ParserATNSimulator> {
+    }
+
+    public static class Parser extends BaseParser {
+
+        public void text() {
+            int _alt = 1;
+            do {
+                switch (_alt) {
+                    case 1:
+                        if (_alt == 1) {
+                            continue;
+                        }
+                        break;
+                    default:
+                        throw new RuntimeException();
+                }
+                _alt = getInterpreter().adaptivePredict();
+            } while (_alt != 2);
+        }
+
+    }}