Cleanup: ChartPoint uses null instead of NaN.

src/main/java/de/dennisguse/opentracks/chart/ChartView.java

@@ -206,7 +206,7 @@ public class ChartView extends View {
                 fontSizeSmall,
                 fontSizeMedium) {
             @Override
-            protected double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
+            protected Double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
                 return chartPoint.getAltitude();
             }
 
@@ -227,7 +227,7 @@ public class ChartView extends View {
                 fontSizeSmall,
                 fontSizeMedium) {
             @Override
-            protected double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
+            protected Double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
                 return chartPoint.getSpeed();
             }
 
@@ -249,7 +249,7 @@ public class ChartView extends View {
                 fontSizeSmall,
                 fontSizeMedium) {
             @Override
-            protected double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
+            protected Double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
                 return chartPoint.getPace();
             }
 
@@ -271,7 +271,7 @@ public class ChartView extends View {
                 fontSizeSmall,
                 fontSizeMedium) {
             @Override
-            protected double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
+            protected Double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
                 return chartPoint.getHeartRate();
             }
 
@@ -292,7 +292,7 @@ public class ChartView extends View {
                 fontSizeSmall,
                 fontSizeMedium) {
             @Override
-            protected double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
+            protected Double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
                 return chartPoint.getCadence();
             }
 
@@ -312,7 +312,7 @@ public class ChartView extends View {
                 fontSizeSmall,
                 fontSizeMedium) {
             @Override
-            protected double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
+            protected Double extractDataFromChartPoint(@NonNull ChartPoint chartPoint) {
                 return chartPoint.getPower();
             }