fix NPE when converting OL with attribute type="circle"

DEVSIX-9452

Author: Alexandr Fedorov

src/test/java/com/itextpdf/html2pdf/css/ListCssTest.java

@@ -74,11 +74,9 @@ public void digitTypeTest() throws IOException, InterruptedException {
         convertToPdfAndCompare("1Type", SOURCE_FOLDER, DESTINATION_FOLDER);
     }
 
-    //TODO: DEVSIX-6128 NullPointerException when trying to convert html with non-existing ol type.
     @Test
-    public void unsupportedType() {
-        Assertions.assertThrows(NullPointerException.class,
-                () -> convertToPdfAndCompare("unsupportedType", SOURCE_FOLDER, DESTINATION_FOLDER));
+    public void unsupportedType() throws IOException, InterruptedException {
+        convertToPdfAndCompare("unsupportedType", SOURCE_FOLDER, DESTINATION_FOLDER);
     }
 
     @Test

src/test/java/com/itextpdf/html2pdf/css/resolve/HtmlStylesToCssConverterTest.java

@@ -62,6 +62,15 @@ public void trimSemicolonsForHeightAttributeTest() {
         assertCssDeclarationListWithOneElement(cssDeclarations, "height", "51%");
     }
 
+    @Test
+    public void invalidAttributeValue() {
+        final Element element = new Element(Tag.valueOf(TagConstants.OL), "");
+        element.attr("type", "circle");
+        JsoupElementNode node = new JsoupElementNode(element);
+        List<CssDeclaration> cssDeclarations = HtmlStylesToCssConverter.convert(node);
+        assertCssDeclarationListWithOneElement(cssDeclarations, "list-style-type", null);
+    }
+
     @Test
     public void withoutSemicolonsHeightAttributeTest() {
         final Element element = new Element(Tag.valueOf(TagConstants.IMG), "");