Java: Prevent extracting method from empty parentheses (IDEA-182482)

java/java-impl/src/com/intellij/refactoring/extractMethod/ExtractMethodProcessor.java

@@ -200,6 +200,7 @@ public class ExtractMethodProcessor implements MatchProvider {
    * Invoked in atomic action
    */
   public boolean prepare(@Nullable Pass<ExtractMethodProcessor> pass) throws PrepareFailedException {
+    if (myElements.length == 0) return false;
     myExpression = null;
     if (myElements.length == 1 && myElements[0] instanceof PsiExpression) {
       final PsiExpression expression = (PsiExpression)myElements[0];

java/java-tests/testData/refactoring/extractMethod/EmptyBlockStatement.java

@@ -0,0 +1,5 @@
+class ExtractEmptyBlock {
+  void foo() {
+    <selection>{}</selection>
+  }
+}

java/java-tests/testSrc/com/intellij/java/refactoring/ExtractMethodTest.java

@@ -1217,6 +1217,10 @@ public class ExtractMethodTest extends LightCodeInsightTestCase {
     doDuplicatesTest();
   }
 
+  public void testEmptyBlockStatement() throws Exception {
+    doExitPointsTest(false);
+  }
+
   private void doTestDisabledParam() throws PrepareFailedException {
     final CommonCodeStyleSettings settings = CodeStyleSettingsManager.getSettings(getProject()).getCommonSettings(JavaLanguage.INSTANCE);
     settings.ELSE_ON_NEW_LINE = true;