Fix crash when saving the last keyframe in the edit gui (fixes #61)

src/integration-test/java/com/replaymod/core/ReplayModIntegrationTest.java

@@ -1,6 +1,7 @@
 package com.replaymod.core;
 
 import com.replaymod.core.regression.RegressionTest60;
+import com.replaymod.core.regression.RegressionTest61;
 import com.replaymod.core.regression.RegressionTest62;
 import com.replaymod.extra.DownloadOpenEye;
 import com.replaymod.online.SkipLogin;
@@ -45,6 +46,7 @@ public class ReplayModIntegrationTest {
                 new LoadReplay(),
 
                 new RegressionTest60(),
+                new RegressionTest61(),
                 new RegressionTest62(),
 
                 // new AbstractTask() {}, // Uncomment to not exit on success (useful for writing more tests)

src/integration-test/java/com/replaymod/core/regression/RegressionTest61.java

@@ -0,0 +1,35 @@
+package com.replaymod.core.regression;
+
+import com.replaymod.core.AbstractTask;
+import com.replaymod.core.CompositeTask;
+import com.replaymod.core.Task;
+import com.replaymod.replay.overlay.OverlayGui;
+import com.replaymod.simplepathing.GuiPathingTasks;
+import com.replaymod.simplepathing.gui.GuiEditKeyframe;
+
+/**
+ * Regression test: #61 NPE when saving in edit keyframe gui of last keyframe
+ */
+public class RegressionTest61 extends CompositeTask {
+    public RegressionTest61() {
+        super(new Task[]{
+                OverlayGui.whileOpened(
+                        // Place keyframe
+                        Task.click(130, 50),
+                        new GuiPathingTasks.ClickPositionKeyframeButton(),
+                        AbstractTask.create(task -> {
+                            // Double click keyframe
+                            task.click(130, 50);
+                            task.click(130, 50);
+                            task.expectGui(GuiEditKeyframe.Position.class, gui -> {
+                                task.click(gui.saveButton);
+                                task.expectPopupClosed(() -> task.future.set(null));
+                            });
+                        }),
+                        // Place second spectator keyframe
+                        new GuiPathingTasks.ClickPositionKeyframeButton()
+                ),
+                new GuiPathingTasks.ClearKeyframeTimeline(),
+        });
+    }
+}

src/main/java/com/replaymod/simplepathing/gui/GuiEditKeyframe.java

@@ -255,6 +255,10 @@ public abstract class GuiEditKeyframe<T extends GuiEditKeyframe<T>> extends Abst
                     xField.getDouble(), yField.getDouble(), zField.getDouble(),
                     yawField.getFloat(), pitchField.getFloat(), rollField.getFloat()
             );
+            if (interpolationPanel.getSettingsPanel() == null) {
+                // The last keyframe doesn't have interpolator settings because there is no segment following it
+                return positionChange;
+            }
             Interpolator interpolator = interpolationPanel.getSettingsPanel().createInterpolator();
             if (interpolationPanel.getInterpolatorType() == InterpolatorType.DEFAULT) {
                 return CombinedChange.createFromApplied(positionChange, timeline.setInterpolatorToDefault(time),