Fix nullness detection on exception variable

core/src/main/java/org/teavm/model/analysis/NullnessInformationBuilder.java

@@ -203,7 +203,7 @@ class NullnessInformationBuilder {
             currentState = new State();
 
             if (block.getExceptionVariable() != null) {
-                notNullVariables.set(block.getIndex());
+                notNullVariables.set(block.getExceptionVariable().getIndex());
             }
 
             currentBlock = block;

core/src/test/java/org/teavm/model/analysis/test/NullnessAnalysisTest.java

@@ -80,6 +80,11 @@ public class NullnessAnalysisTest {
         test();
     }
 
+    @Test
+    public void exception() {
+        test();
+    }
+
     private void test() {
         String baseName = "model/analysis/nullness/" + name.getMethodName();
         String originalResourceName = baseName + ".original.txt";

core/src/test/resources/model/analysis/nullness/exception.extended.txt

@@ -0,0 +1,12 @@
+var @this as this
+$start
+    @str := invokeStatic `Foo.getData()Ljava/lang/String;`
+    @n := invokeStatic `java.lang.Integer.parseInt(Ljava/lang/String;)I` @str
+    return @n
+    catch java.lang.RuntimeException goto $handle
+$handle
+    @e := exception
+    @m := invoke `java.lang.Throwable.getMessage()Ljava/lang/String;` @e
+    @z := invoke `java.lang.String.length()I` @m
+    @m_1 := nullCheck @m
+    return @z

core/src/test/resources/model/analysis/nullness/exception.original.txt

@@ -0,0 +1,11 @@
+var @this as this
+$start
+    @str := invokeStatic `Foo.getData()Ljava/lang/String;`
+    @n := invokeStatic `java.lang.Integer.parseInt(Ljava/lang/String;)I` @str
+    return @n
+    catch java.lang.RuntimeException goto $handle
+$handle
+    @e := exception
+    @m := invoke `java.lang.Throwable.getMessage()Ljava/lang/String;` @e
+    @z := invoke `java.lang.String.length()I` @m
+    return @z