Fix review comments and design

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

@@ -61,7 +61,9 @@ public static Handler buildDefault(Config config) {
     handlerListBuilder.add(libraryModelsHandler);
     handlerListBuilder.add(StreamNullabilityPropagatorFactory.getRxStreamNullabilityPropagator());
     handlerListBuilder.add(StreamNullabilityPropagatorFactory.getJavaStreamNullabilityPropagator());
-    handlerListBuilder.add(libraryModelsHandler.getStreamNullabilityPropagatorFromModels());
+    handlerListBuilder.add(
+        StreamNullabilityPropagatorFactory.fromSpecs(
+            libraryModelsHandler.getStreamNullabilitySpecs()));
     handlerListBuilder.add(new ContractHandler(config));
     handlerListBuilder.add(new ApacheThriftIsSetHandler());
     handlerListBuilder.add(new GrpcHandler());

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

@@ -294,18 +294,22 @@ private void setUnconditionalArgumentNullness(
   }
 
   /**
-   * Generate a StreamNullabilityPropagator handler based on all the stream specifications loaded
-   * from any of our library models.
+   * Get all the stream specifications loaded from any of our library models.
    *
-   * <p>This handler must be registered in Handlers.java separatedly from the LibraryModelsHandler
-   * itself.
+   * <p>This is used in Handlers.java to create a StreamNullabilityPropagator handler, which gets
+   * registered independently of this LibraryModelsHandler itself.
+   *
+   * <p>LibraryModelsHandler is responsible from reading the library models for stream specs, but
+   * beyond that, checking of the specs falls under the responsibility of the generated
+   * StreamNullabilityPropagator handler.
+   *
+   * @return The list of all stream specifications loaded from any of our library models.
    */
-  public StreamNullabilityPropagator getStreamNullabilityPropagatorFromModels() {
+  public ImmutableList<StreamTypeRecord> getStreamNullabilitySpecs() {
     // Note: Currently, OptimizedLibraryModels doesn't carry the information about stream type
-    // records,
-    // it is not clear what it means to "optimize" lookup for those and they get access only once:
-    // here.
-    return new StreamNullabilityPropagator(libraryModels.customStreamNullabilitySpecs());
+    // records, it is not clear what it means to "optimize" lookup for those and they get accessed
+    // only once by calling this method during handler setup in Handlers.java.
+    return libraryModels.customStreamNullabilitySpecs();
   }
 
   private static LibraryModels loadLibraryModels(Config config) {

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

@@ -29,6 +29,8 @@
 import com.uber.nullaway.handlers.stream.StreamTypeRecord;
 
 public class StreamNullabilityPropagatorFactory {
+
+  /** Returns a handler for the standard Java 8 stream APIs. */
   public static StreamNullabilityPropagator getJavaStreamNullabilityPropagator() {
     ImmutableList<StreamTypeRecord> streamModels =
         StreamModelBuilder.start()
@@ -78,6 +80,7 @@ public static StreamNullabilityPropagator getJavaStreamNullabilityPropagator() {
     return new StreamNullabilityPropagator(streamModels);
   }
 
+  /** Returns a handler for io.reactivex.* stream APIs */
   public static StreamNullabilityPropagator getRxStreamNullabilityPropagator() {
     ImmutableList<StreamTypeRecord> rxModels =
         StreamModelBuilder.start()
@@ -137,4 +140,19 @@ public static StreamNullabilityPropagator getRxStreamNullabilityPropagator() {
 
     return new StreamNullabilityPropagator(rxModels);
   }
+
+  /**
+   * Create a new StreamNullabilityPropagator from a list of StreamTypeRecord specs.
+   *
+   * <p>This is used to create a new StreamNullabilityPropagator based on stream API specs provided
+   * by library models.
+   *
+   * @param streamNullabilitySpecs the list of StreamTypeRecord objects defining one or more stream
+   *     APIs (from {@link StreamModelBuilder}).
+   * @return A handler corresponding to the stream APIs defined by the given specs.
+   */
+  public static StreamNullabilityPropagator fromSpecs(
+      ImmutableList<StreamTypeRecord> streamNullabilitySpecs) {
+    return new StreamNullabilityPropagator(streamNullabilitySpecs);
+  }
 }

nullaway/src/main/java/com/uber/nullaway/handlers/stream/StreamModelBuilder.java

@@ -92,6 +92,12 @@ public StreamModelBuilder addStreamType(TypePredicate tp) {
     return this;
   }
 
+  /**
+   * Add a stream type to our models based on the type's fully qualified name.
+   *
+   * @param fullyQualifiedName the FQN of the class/interface in our stream-based API.
+   * @return This builder (for chaining).
+   */
   public StreamModelBuilder addStreamTypeFromName(String fullyQualifiedName) {
     return this.addStreamType(new DescendantOf(Suppliers.typeFromString(fullyQualifiedName)));
   }