IDEA-139645 diff: it's OK to have nullable color for 'error stripe markers'

platform/diff-impl/src/com/intellij/diff/util/TextDiffType.java

@@ -42,6 +42,6 @@ public interface TextDiffType {
   @NotNull
   Color getIgnoredColor(@Nullable Editor editor);
 
-  @NotNull
+  @Nullable
   Color getMarkerColor(@Nullable Editor editor);
 }

platform/diff-impl/src/com/intellij/diff/util/TextDiffTypeFactory.java

@@ -102,7 +102,7 @@ public class TextDiffTypeFactory {
       }
     }
 
-    @NotNull
+    @Nullable
     @Override
     public Color getMarkerColor(@Nullable Editor editor) {
       return getAttributes(editor).getErrorStripeColor();