fixed yellow code in PersistentFSImpl where VEvent was casted to subclass for the method different not-nullness

java/java-tests/testData/inspection/redundantCast/generics/DifferentNullness/expected.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<problems>
+  <problem>
+    <file>A.java</file>
+    <line>5</line>
+    <problem_class>Redundant type cast</problem_class>
+    <description>Casting &lt;code&gt;a&lt;/code&gt; to &lt;code&gt;AA&lt;/code&gt; is redundant</description>
+  </problem>
+</problems>

java/java-tests/testData/inspection/redundantCast/generics/DifferentNullness/src/A.java

@@ -0,0 +1,32 @@
+import org.jetbrains.annotations.*;
+
+class A {
+  static String doit(A a) {
+    String d = ((AA)a).danuna();
+    String notNull = ((AA)a).doadd();
+    return notNull + d;
+  }
+
+  @Nullable
+  String doadd() {
+    return null;
+  }
+
+  @NotNull
+  String danuna() {
+    return "";
+  }
+}
+
+class AA extends A {
+  @NotNull
+  String doadd() {
+    return "";
+  }
+
+  @Override
+  @NotNull
+  String danuna() {
+    return "";
+  }
+}