Make class-level caches for InferredJARModelsHandler instance fields. (…

…#315)

Static mutable fields are incredibly dangerous in NullAway and should have been avoided. The original code actually triggers a crash when using a shared classloader for Error Prone.

nullaway/src/main/java/com/uber/nullaway/handlers/InferredJARModelsHandler.java

@@ -72,9 +72,9 @@ private static void LOG(boolean cond, String tag, String msg) {
 
   private static final int RETURN = -1; // '-1' indexes Return type in the Annotation Cache
 
-  private static Map<String, Map<String, Map<Integer, Set<String>>>> argAnnotCache;
-  private static Map<String, Set<String>> mapModelJarLocations;
-  private static Set<String> loadedJars;
+  private final Map<String, Map<String, Map<Integer, Set<String>>>> argAnnotCache;
+  private final Map<String, Set<String>> mapModelJarLocations;
+  private final Set<String> loadedJars;
 
   private final Config config;