fix: Fix issue with null date

refactor: Update CveProject model to handle multiple cvss versions

src/main/java/org/eclipsefoundation/cve/model/CveData.java

@@ -34,6 +34,7 @@ public abstract class CveData {
 
     public abstract String getId();
 
+    @Nullable
     public abstract LocalDate getDatePublished();
 
     public abstract String getProject();
@@ -66,7 +67,7 @@ public abstract class CveData {
     public abstract static class Builder {
         public abstract Builder setId(String id);
 
-        public abstract Builder setDatePublished(LocalDate date);
+        public abstract Builder setDatePublished(@Nullable LocalDate date);
 
         public abstract Builder setProject(String project);