PY-12360 Do not add extra blank line at the end of empty file

python/src/com/jetbrains/python/formatter/PyTrailingBlankLinesPostFormatProcessor.java

@@ -110,7 +110,7 @@ public class PyTrailingBlankLinesPostFormatProcessor implements PostFormatProces
       }
       documentManager.doPostponedOperationsAndUnblockDocument(document);
       final String text = StringUtil.repeat("\n", numLineFeeds);
-      if (numLineFeeds > 0) {
+      if (numLineFeeds > 0 && whitespaceRange.getStartOffset() != 0) {
         if (!whitespaceRange.isEmpty()) {
           document.replaceString(whitespaceRange.getStartOffset(), whitespaceRange.getEndOffset(), text);
         }

python/testSrc/com/jetbrains/python/PyFormatterTest.java

@@ -562,6 +562,11 @@ public class PyFormatterTest extends PyTestCase {
     doTest();
   }
 
+  // PY-11552
+  public void testTrailingBlankLinesInEmptyFile() {
+    doTest();
+  }
+
   // PY-15530
   public void testAlignmentInArgumentListWhereFirstArgumentIsEmptyCall() {
     doTest();