add exception handling

src/main/java/com/faf223/expensetrackerfaf/util/exceptions/TransactionDoesNotBelongToTheUserException.java

@@ -0,0 +1,7 @@
+package com.faf223.expensetrackerfaf.util.exceptions;
+
+public class TransactionDoesNotBelongToTheUserException extends RuntimeException {
+    public TransactionDoesNotBelongToTheUserException(String message) {
+        super(message);
+    }
+}

src/main/java/com/faf223/expensetrackerfaf/util/exceptions/TransactionNotCreatedException.java

@@ -0,0 +1,7 @@
+package com.faf223.expensetrackerfaf.util.exceptions;
+
+public class TransactionNotCreatedException extends RuntimeException {
+    public TransactionNotCreatedException(String message) {
+        super(message);
+    }
+}

src/main/java/com/faf223/expensetrackerfaf/util/exceptions/TransactionNotUpdatedException.java

@@ -0,0 +1,7 @@
+package com.faf223.expensetrackerfaf.util.exceptions;
+
+public class TransactionNotUpdatedException extends RuntimeException {
+    public TransactionNotUpdatedException(String message) {
+        super(message);
+    }
+}

src/main/java/com/faf223/expensetrackerfaf/util/exceptions/TransactionsNotFoundException.java

@@ -0,0 +1,7 @@
+package com.faf223.expensetrackerfaf.util.exceptions;
+
+public class TransactionsNotFoundException extends RuntimeException {
+    public TransactionsNotFoundException(String message) {
+        super(message);
+    }
+}

src/main/java/com/faf223/expensetrackerfaf/util/exceptions/UserNotFoundException.java

@@ -0,0 +1,7 @@
+package com.faf223.expensetrackerfaf.util.exceptions;
+
+public class UserNotFoundException extends RuntimeException {
+    public UserNotFoundException(String message) {
+        super(message);
+    }
+}