NullTernary shouldn't crash on JDK 14

check_api/src/main/java/com/google/errorprone/util/ASTHelpers.java

@@ -1565,8 +1565,15 @@ public Type visitAnnotation(AnnotationTree tree, Void unused) {
 
     @Override
     public Type visitCase(CaseTree tree, Void unused) {
-      SwitchTree switchTree = (SwitchTree) parent.getParentPath().getLeaf();
-      return getType(switchTree.getExpression());
+      Tree t = parent.getParentPath().getLeaf();
+      // JDK 12+, t can be SwitchExpressionTree
+      if (t instanceof SwitchTree) {
+        SwitchTree switchTree = (SwitchTree) t;
+        return getType(switchTree.getExpression());
+      }
+      // TODO(bhagwani): When the ErrorProne project switches to JDK 12, we should check
+      // for SwitchExpressionTree.
+      return null;
     }
 
     @Override

check_api/src/main/java/com/google/errorprone/util/RuntimeVersion.java

@@ -75,6 +75,11 @@ public static boolean isAtLeast13() {
     return MAJOR >= 13;
   }
 
+  /** Returns true if the current runtime is JDK 14 or newer. */
+  public static boolean isAtLeast14() {
+    return MAJOR >= 14;
+  }
+
   /** Returns true if the current runtime is JDK 15 or newer. */
   public static boolean isAtLeast15() {
     return MAJOR >= 15;

core/src/test/java/com/google/errorprone/bugpatterns/NullTernaryTest.java

@@ -16,7 +16,10 @@
 
 package com.google.errorprone.bugpatterns;
 
+import static org.junit.Assume.assumeTrue;
+
 import com.google.errorprone.CompilationTestHelper;
+import com.google.errorprone.util.RuntimeVersion;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -121,4 +124,25 @@ public void conditionalInCondition() {
             "}")
         .doTest();
   }
+
+  @Test
+  public void expressionSwitch_doesNotCrash() {
+    assumeTrue(RuntimeVersion.isAtLeast14());
+    testHelper
+        .addSourceLines(
+            "Test.java",
+            "class Test {",
+            " static String doStuff(SomeEnum enumVar) {",
+            "   return switch (enumVar) {",
+            "     case A -> enumVar.name() != null ? \"AAA\" : null;",
+            "     default -> null;",
+            "   };",
+            " }",
+            " ",
+            " static enum SomeEnum {",
+            "   A, B",
+            " }",
+            "}")
+        .doTest();
+  }
 }