handleFlush: do not use inherent nullability for unknown values

Fixes IDEA-172844 False positive "Method invocation 'methodName' may produce NPE" in while loop condition

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DfaMemoryStateImpl.java

@@ -269,7 +269,8 @@ public class DfaMemoryStateImpl implements DfaMemoryState {
 
   private DfaValue handleFlush(DfaVariableValue flushed, DfaValue value) {
     if (value instanceof DfaVariableValue && (value == flushed || myFactory.getVarFactory().getAllQualifiedBy(flushed).contains(value))) {
-      Nullness nullability = isNotNull(value) ? Nullness.NOT_NULL : ((DfaVariableValue)value).getInherentNullability();
+      Nullness nullability = isNotNull(value) ? Nullness.NOT_NULL :
+                             isUnknownState(value) ? Nullness.UNKNOWN : ((DfaVariableValue)value).getInherentNullability();
       return myFactory.createTypeValue(((DfaVariableValue)value).getVariableType(), nullability);
     }
     return value;

java/java-tests/testData/inspection/dataFlow/fixture/NullableGetterInLoop.java

@@ -0,0 +1,27 @@
+import org.jetbrains.annotations.*;
+
+// IDEA-172844
+abstract class SimpleClass {
+
+  @Nullable
+  protected MyType findSelfOrInnerByNonQualifiedName() {
+    MyType nearestOuter = getOwnerParentOfType(MyType.class);
+    if (nearestOuter != null) {
+      MyType currentOuter = nearestOuter;
+      while (currentOuter.getOuterClass() != null) { // False positive error here
+        currentOuter = currentOuter.getOuterClass();
+      }
+    }
+
+    return null;
+  }
+
+  @Nullable
+  abstract MyType getOwnerParentOfType(Class<MyType> apexPsiTypeDeclarationClass);
+
+  static abstract class MyType {
+
+    @Nullable
+    abstract MyType getOuterClass();
+  }
+}

java/java-tests/testSrc/com/intellij/java/codeInspection/DataFlowInspectionTest.java

@@ -583,4 +583,5 @@ public class DataFlowInspectionTest extends DataFlowInspectionTestCase {
   public void testLessThanRelations() { doTest(); }
   public void testAdvancedArrayAccess() { doTest(); }
   public void testNullabilityBasics() { doTest(); }
+  public void testNullableGetterInLoop() { doTest(); }
 }