We need ProcessingError in repository.

demo/03/src/main/java/pl/amu/edu/demo/either/ProcessingError.java

@@ -0,0 +1,11 @@
+package pl.amu.edu.demo.either;
+
+
+import lombok.AllArgsConstructor;
+import lombok.ToString;
+
+@AllArgsConstructor(staticName = "of")
+@ToString
+public class ProcessingError {
+    private final String errorMessage;
+}