Add positive case and make sure it reports an error.

nullaway/src/main/java/com/uber/nullaway/LibraryModels.java

@@ -136,9 +136,9 @@ public interface LibraryModels {
    *
    * <p>This allows users to define filter/map/other methods for APIs which behave similarly to Java
    * 8 streams or ReactiveX streams, so that NullAway is able to understand nullability invariants
-   * across stream API calls. See {@see com.uber.nullaway.handlers.stream.StreamModelBuilder} for
-   * details on how to construct these {@see com.uber.nullaway.handlers.stream.StreamTypeRecord}
-   * specs. A full example is available at {@see
+   * across stream API calls. See {@link com.uber.nullaway.handlers.stream.StreamModelBuilder} for
+   * details on how to construct these {@link com.uber.nullaway.handlers.stream.StreamTypeRecord}
+   * specs. A full example is available at {@link
    * com.uber.nullaway.testlibrarymodels.TestLibraryModels}.
    *
    * @return A list of StreamTypeRecord specs (usually generated using StreamModelBuilder).

nullaway/src/test/resources/com/uber/nullaway/testdata/NullAwayStreamSupportNegativeCases.java

@@ -294,6 +294,13 @@ private CustomStream<Integer> filterThenMapLambdasCustomStream(CustomStream<Stri
     return stream.filter(s -> s != null).map(s -> s.length());
   }
 
+  private CustomStream<Integer> filterThenMapNullableContainerLambdasCustomStream(
+            CustomStream<NullableContainer<String>> stream) {
+        return stream
+                .filter(c -> c.get() != null)
+                .map(c -> c.get().length());
+    }
+
   private CustomStream<Integer> filterThenMapMethodRefsCustomStream(
       CustomStream<NullableContainer<String>> stream) {
     return stream

nullaway/src/test/resources/com/uber/nullaway/testdata/NullAwayStreamSupportPositiveCases.java

@@ -23,6 +23,7 @@
 package com.uber.nullaway.testdata;
 
 import com.google.common.base.Preconditions;
+import com.uber.nullaway.testdata.unannotated.CustomStreamWithoutModel;
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.stream.DoubleStream;
@@ -153,6 +154,28 @@ private void forEachOrdered(Stream<NullableContainer<String>> stream) {
     stream.forEachOrdered(s -> System.out.println(s.get().length()));
   }
 
+  // CustomStreamWithoutModel is NOT modeled in TestLibraryModels
+  private CustomStreamWithoutModel<Integer> filterThenMapLambdasCustomStream(CustomStreamWithoutModel<String> stream) {
+    // Safe because generic is String, not @Nullable String
+    return stream.filter(s -> s != null).map(s -> s.length());
+  }
+
+  private CustomStreamWithoutModel<Integer> filterThenMapNullableContainerLambdasCustomStream(
+          CustomStreamWithoutModel<NullableContainer<String>> stream) {
+    return stream
+            .filter(c -> c.get() != null)
+            // BUG: Diagnostic contains: dereferenced expression
+            .map(c -> c.get().length());
+  }
+
+  private CustomStreamWithoutModel<Integer> filterThenMapMethodRefsCustomStream(
+          CustomStreamWithoutModel<NullableContainer<String>> stream) {
+    return stream
+            .filter(c -> c.get() != null && perhaps())
+            .map(NullableContainer::get) // CSWoM<NullableContainer<String>> -> CSWoM<@Nullable String>
+            .map(String::length); // Should be an error with proper generics support!
+  }
+
   private static class CheckNonfinalBeforeStream<T> {
     @Nullable private T ref;
 

nullaway/src/test/resources/com/uber/nullaway/testdata/unannotated/CustomStreamWithoutModel.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2023 Uber Technologies, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.uber.nullaway.testdata.unannotated;
+
+import java.util.function.Function;
+import java.util.function.Predicate;
+
+/**
+ * A copy of {@link CustomStream} but for which our test library models have no spec/model, to test that errors still
+ * get reported in the absence of a model.
+ */
+public class CustomStreamWithoutModel<T> {
+
+    private CustomStreamWithoutModel() {}
+
+    public CustomStreamWithoutModel<T> filter(Predicate<? super T> predicate) {
+        throw new UnsupportedOperationException();
+    }
+
+    public <R> CustomStreamWithoutModel<R> map(Function<? super T, ? extends R> mapper) {
+        throw new UnsupportedOperationException();
+    }
+}

test-library-models/src/main/java/com/uber/nullaway/testlibrarymodels/TestLibraryModels.java

@@ -96,7 +96,7 @@ public ImmutableList<StreamTypeRecord> customStreamNullabilitySpecs() {
     // Identical to the default model for java.util.stream.Stream, but with the original type
     // renamed
     return StreamModelBuilder.start()
-        .addStreamTypeFromName("com.uber.unannotated.CustomStreamA")
+        .addStreamTypeFromName("com.uber.nullaway.testdata.unannotated.CustomStream")
         .withFilterMethodFromSignature("filter(java.util.function.Predicate<? super T>)")
         .withMapMethodFromSignature(
             "<R>map(java.util.function.Function<? super T,? extends R>)",