Added few validation in call api

src/main/java/net/gepafin/tendermanagement/util/FieldValidator.java

@@ -37,4 +37,9 @@ public class FieldValidator {
 			throw new ValidationException(Status.VALIDATION_ERROR, errors);
 		}
 	}
+
+	public FieldValidator addError( String errorMessage) {
+		errors.add(errorMessage);
+		return this;
+	}
 }