Adds proper handling of empty properties in CssFontFaceRule

DEVSIX-6339

Author: glenn.volckaert

styled-xml-parser/src/main/java/com/itextpdf/styledxmlparser/css/CssFontFaceRule.java

@@ -71,7 +71,10 @@ public CssFontFaceRule() {
      * @return the properties
      */
     public List<CssDeclaration> getProperties() {
-        return new ArrayList<>(properties) ;
+        if (properties==null) {
+            return new ArrayList<>();
+        }
+        return new ArrayList<>(properties);
     }
 
     /* (non-Javadoc)
@@ -89,7 +92,7 @@ public void addBodyCssDeclarations(List<CssDeclaration> cssDeclarations) {
     public String toString() {
         StringBuilder sb = new StringBuilder();
         sb.append("@").append(getRuleName()).append(" {").append("\n");
-        for (CssDeclaration declaration : properties) {
+        for (CssDeclaration declaration : getProperties()) {
             sb.append("    ");
             sb.append(declaration);
             sb.append(";\n");

styled-xml-parser/src/main/java/com/itextpdf/styledxmlparser/css/parse/syntax/CssParserStateController.java

@@ -344,7 +344,7 @@ void storeSemicolonAtRule() {
     void finishAtRuleBlock() {
         List<CssDeclaration> storedProps = storedPropertiesWithoutSelector.pop();
         CssNestedAtRule atRule = nestedAtRules.pop();
-        if (isCurrentRuleSupported) {
+        if (isCurrentRuleSupported ) {
             processFinishedAtRuleBlock(atRule);
             if (!storedProps.isEmpty()) {
                 atRule.addBodyCssDeclarations(storedProps);