Merge pull request #10 from gry79/fix-characteristics

Fix NPE in HoldPositionCharacteristic and null value in serialized characteristics

Author: andylintner

src/main/java/com/beowulfe/hap/characteristics/BaseCharacteristic.java

@@ -172,7 +172,7 @@ protected void setJsonValue(JsonObjectBuilder builder, T value) {
 		} else if (value instanceof BigDecimal){
 			builder.add("value", (BigDecimal) value);
 		} else if (value == null) {
-			builder.addNull("value");
+			// Do not add null value, HomeKit cannot handle that
 		} else {
 			builder.add("value", value.toString());
 		}

src/main/java/com/beowulfe/hap/impl/characteristics/windowcovering/HoldPositionCharacteristic.java

@@ -22,7 +22,7 @@ protected void setValue(Boolean value) throws Exception {
 	@Override
 	protected CompletableFuture<Boolean> getValue() {
 		//Write only
-		return null;
+		return CompletableFuture.completedFuture(null);
 	}
 
 }