Add default options for the enqueueing form

Adds defaults for requestType and assignment. Corrects validation
to handle empty values properly.

src/main/java/nl/tudelft/ewi/queue/model/Request.java

@@ -69,6 +69,7 @@ public class Request implements RecordsEvents<Request>, Serializable, Comparable
 	@JsonView(View.Summary.class)
 	private Room room;
 
+	@NotNull
 	@JsonView(View.Summary.class)
 	@OneToOne
 	private RequestType requestType;

src/main/java/nl/tudelft/ewi/queue/model/RequestType.java

@@ -24,6 +24,8 @@ import javax.validation.constraints.Size;
 
 import nl.tudelft.ewi.queue.views.View;
 
+import org.hibernate.validator.constraints.NotBlank;
+
 import com.fasterxml.jackson.annotation.JsonView;
 
 @Entity
@@ -35,6 +37,7 @@ public class RequestType implements Serializable {
 	@GeneratedValue
 	private Long id;
 
+	@NotBlank
 	@JsonView(View.Summary.class)
 	@Size(max = 250)
 	private String name;

src/main/resources/templates/lab/enqueue.html

@@ -70,6 +70,7 @@
             <div class="col-sm-8">
                 <select class="form-control" th:classappend="${#fields.hasErrors('assignment')} ? 'is-invalid'"
                         id="inputAssignment" th:field="*{assignment}">
+                    <option value="" th:selected="selected">Choose an assignment</option>
                     <option th:each="assignment : ${lab.assignments}" th:value="${assignment.id}"
                             th:text="${assignment.name}">Assembly programming
                     </option>
@@ -101,6 +102,7 @@
             <div class="col-sm-8">
                 <select class="form-control" id="inputType" th:field="*{requestType}"
                         th:classappend="${#fields.hasErrors('requestType')} ? 'is-invalid'">
+                    <option value="" th:selected="selected">Choose the type</option>
                     <option th:each="requestType : ${lab.allowedRequestTypes}" th:value="${requestType.id}"
                             th:text="${requestType.name}"></option>
                 </select>