Replace JSR 305 annotations (#386)

* Replace Nullable with equivalent from Checker

Closes #385

src/main/java/org/kiwiproject/test/mongo/MongoTestProperties.java

@@ -19,10 +19,9 @@
 import lombok.Builder;
 import lombok.Value;
 import org.apache.commons.lang3.math.NumberUtils;
+import org.checkerframework.checker.nullness.qual.Nullable;
 import org.kiwiproject.net.KiwiUrls;
 
-import javax.annotation.Nullable;
-
 /**
  * Simple value class that contains properties related to connecting to Mongo in the context of a service that uses
  * MongoDB for persistence. The constructor and builder accept a service/application name and host, which helps to