Fix null pointers in sendable chooser stuff (#449)

Was caused by the combobox getting de-selected and setting the selected option to null instead of the default option

Author: SamCarlberg

plugins/base/src/main/java/edu/wpi/first/shuffleboard/plugin/base/data/SendableChooserData.java

@@ -5,6 +5,7 @@
 
 import java.util.Arrays;
 import java.util.Map;
+import java.util.Objects;
 
 /**
  * Represents data options sent by the robot that may be selected by the drivers.
@@ -32,9 +33,9 @@ public SendableChooserData(Map<String, Object> map) {
 
   @SuppressWarnings("JavadocMethod")
   public SendableChooserData(String[] options, String defaultOption, String selectedOption) {
-    this.options = options.clone();
-    this.defaultOption = defaultOption;
-    this.selectedOption = selectedOption;
+    this.options = Objects.requireNonNull(options, "options").clone();
+    this.defaultOption = Objects.requireNonNull(defaultOption, "defaultOption");
+    this.selectedOption = Objects.requireNonNull(selectedOption, "selectedOption");
   }
 
   public String[] getOptions() {

plugins/base/src/main/java/edu/wpi/first/shuffleboard/plugin/base/widget/ComboBoxChooserWidget.java

@@ -1,13 +1,13 @@
 package edu.wpi.first.shuffleboard.plugin.base.widget;
 
+import edu.wpi.first.shuffleboard.api.widget.ComplexAnnotatedWidget;
+import edu.wpi.first.shuffleboard.api.widget.Description;
+import edu.wpi.first.shuffleboard.api.widget.ParametrizedController;
 import edu.wpi.first.shuffleboard.plugin.base.data.SendableChooserData;
 import edu.wpi.first.shuffleboard.plugin.base.data.types.SendableChooserType;
 
 import java.util.Map;
 
-import edu.wpi.first.shuffleboard.api.widget.ComplexAnnotatedWidget;
-import edu.wpi.first.shuffleboard.api.widget.Description;
-import edu.wpi.first.shuffleboard.api.widget.ParametrizedController;
 import javafx.fxml.FXML;
 import javafx.scene.control.ComboBox;
 import javafx.scene.layout.Pane;
@@ -37,7 +37,16 @@ private void initialize() {
     });
     comboBox.getSelectionModel()
         .selectedItemProperty()
-        .addListener((__, oldValue, newValue) -> setData(getData().withSelectedOption(newValue)));
+        .addListener((__, oldValue, newValue) -> {
+          SendableChooserData currentData = getData();
+          if (newValue == null) {
+            String defaultOption = currentData.getDefaultOption();
+            setData(currentData.withSelectedOption(defaultOption));
+            comboBox.getSelectionModel().select(defaultOption);
+          } else {
+            setData(currentData.withSelectedOption(newValue));
+          }
+        });
   }
 
   private void updateOptions(String... options) {