Make it easier to deserialise from a Map to ImmutableCapabilities

We do this by sacrificing a certain amount of type safety
in the constructor, but we then enforce this at run time.

java/client/src/org/openqa/selenium/ImmutableCapabilities.java

@@ -72,8 +72,13 @@ public ImmutableCapabilities(Capabilities other) {
     this(other.asMap());
   }
 
-  public ImmutableCapabilities(Map<String, ?> capabilities) {
-    capabilities.forEach(this::setCapability);
+  public ImmutableCapabilities(Map<?, ?> capabilities) {
+    capabilities.forEach((key, value) -> {
+      if (!(key instanceof String)) {
+        throw new IllegalArgumentException("Key values must be strings");
+      }
+      setCapability(String.valueOf(key), value);
+    });
   }
 
   public static ImmutableCapabilities copyOf(Capabilities capabilities) {

java/server/src/org/openqa/selenium/grid/data/NodeStatus.java

@@ -145,9 +145,8 @@ private static Map<Capabilities, Integer> readCapacityNamed(
     ImmutableMap.Builder<Capabilities, Integer> capacity = ImmutableMap.builder();
     kind.forEach(obj -> {
       Map<?, ?> cap = (Map<?, ?>) obj;
-      //noinspection unchecked
       capacity.put(
-          new ImmutableCapabilities((Map<String, Object>) cap.get("capabilities")),
+          new ImmutableCapabilities((Map<?, ?>) cap.get("capabilities")),
           ((Number) cap.get("count")).intValue());
     });
 

java/server/src/org/openqa/selenium/grid/data/Session.java

@@ -70,9 +70,7 @@ private Map<String, Object> toJson() {
   private static Session fromJson(Map<String, Object> raw) throws URISyntaxException {
     SessionId id = new SessionId((String) raw.get("sessionId"));
     URI uri = new URI((String) raw.get("uri"));
-    @SuppressWarnings("unchecked")
-    Map<String, Object> rawCaps = (Map<String, Object>) raw.get("capabilities");
-    Capabilities caps = new ImmutableCapabilities(rawCaps);
+    Capabilities caps = new ImmutableCapabilities((Map<?, ?>) raw.get("capabilities"));
 
     return new Session(id, uri, caps);
   }