feat: added throw exceptions to DonationRepository

src/main/java/edu/group5/app/model/donation/DonationRepository.java

@@ -25,6 +25,9 @@ public class DonationRepository extends DBRepository<Integer, Donation> {
    *                where the key represents the donation ID
    */
   public DonationRepository(HashMap<Integer, Donation> content){
+    if (content == null) {
+      throw new IllegalArgumentException("Content cannot be null");
+    }
     super(content);
     this.content = content;
   }
@@ -42,7 +45,10 @@ public DonationRepository(HashMap<Integer, Donation> content){
    * {@code false} if a donation with the same ID already exists
    */
   public boolean addDonation(Donation donation) {
-    if(content.containsKey(donation.donationId())){
+    if (donation == null) {
+      throw new IllegalArgumentException("Donation cannot be null");
+    }
+    if (content.containsKey(donation.donationId())){
       return false;
     }
     content.put(donation.donationId(), donation);
@@ -97,6 +103,9 @@ public HashMap<Integer, Donation> sortByAmount() {
    * @return a map containing all donations that belong to the given organization
    */
   public HashMap<Integer, Donation> filterByOrganization(int orgNumber) {
+    if (orgNumber <= 0) {
+      throw new IllegalArgumentException("Organization number must be positive");
+    }
     return content.entrySet()
         .stream()
         .filter(entry -> entry.getValue().organizationId()  == orgNumber)