added null checks to validator, created a bunch of junit tests

desktop/src/main/java/org/example/petshopdesktop/Validator.java

@@ -13,6 +13,7 @@ public class Validator {
         if (value == null || value.isBlank()){
             msg += name + " is required. \n";
         }
+
         return msg;
     }
 
@@ -24,8 +25,13 @@ public class Validator {
      */
     public static String isNonNegativeDouble(String value, String name){
         String msg ="";
+        if (value == null) {
+            msg += name + " must be a number.\n";
+
+            return msg;
+        }
         double result;
-        try{
+        try {
             result = Double.parseDouble(value);
             if (result < 0){
                 msg += name + " must be greater than or equal 0. \n";
@@ -34,6 +40,7 @@ public class Validator {
         catch (NumberFormatException e){
             msg += name + " must be a number.\n";
         }
+
         return msg;
     }
 
@@ -47,8 +54,13 @@ public class Validator {
      */
     public static String isDoubleInRange(String value, String name, double minValue, double maxValue){
         String msg ="";
+        if (value == null) {
+            msg += name + " must be a number.\n";
+
+            return msg;
+        }
         double result;
-        try{
+        try {
             result = Double.parseDouble(value);
             if (result < minValue || result > maxValue){
                 msg += name + " must be between " + minValue + " and " + maxValue + "\n";
@@ -57,6 +69,7 @@ public class Validator {
         catch (NumberFormatException e){
             msg += name + " must be a number.\n";
         }
+
         return msg;
     }
 
@@ -69,7 +82,7 @@ public class Validator {
     public static String isNonNegativeInteger(String value, String name){
         String msg ="";
         int result;
-        try{
+        try {
             result = Integer.parseInt(value);
             if (result < 0){
                 msg += name + " must be greater than or equal 0. \n";
@@ -78,6 +91,7 @@ public class Validator {
         catch (NumberFormatException e){
             msg += name + " must be a whole number.\n";
         }
+
         return msg;
     }
 
@@ -90,9 +104,10 @@ public class Validator {
      */
     public static String isLessThanVarChars(String value, String name, int length){
         String msg ="";
-        if (value.length() > length){
+        if (value == null || value.length() > length){
             msg += name + " must be less than " + length + " characters. \n";
         }
+
         return msg;
     }
 
@@ -104,11 +119,17 @@ public class Validator {
      */
     public static String isValidEmail(String value, String name){
         String msg = "";
+        if (value == null) {
+            msg += name + " is not in a valid format. \n";
+
+            return msg;
+        }
         String regex = "^[A-Za-z0-9+_.-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}$";
 
         if (!value.matches(regex)){
             msg += name + " is not in a valid format. \n";
         }
+
         return msg;
     }
 
@@ -120,11 +141,17 @@ public class Validator {
      */
     public static String isValidPhoneNumber(String value, String name){
         String msg = "";
+        if (value == null) {
+            msg += name + " must be in format XXX-XXX-XXXX. \n";
+
+            return msg;
+        }
         String regex = "^\\d{3}-\\d{3}-\\d{4}$";
 
         if (!value.matches(regex)){
             msg += name + " must be in format XXX-XXX-XXXX. \n";
         }
+
         return msg;
     }
-}
+}