JSpecify: fix crash with calls to static methods (#856)

After adding com.google.common to annotated packages for
buildWithNullAway in JSpecify Mode, we got the following exception:

```java

error: An unhandled exception was thrown by the Error Prone static analysis plugin.
    return findEnclosingMethodOrLambdaOrInitializer(path, ImmutableSet.of());

com.google.common.util.concurrent.UncheckedExecutionException: java.lang.NullPointerException: castToNonNull failed!
        at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2086)
        at com.google.common.cache.LocalCache.get(LocalCache.java:4012)
        at com.google.common.cache.LocalCache.getOrLoad(LocalCache.java:4035)
        at com.google.common.cache.LocalCache$LocalLoadingCache.get(LocalCache.java:5011)

Caused by: java.lang.NullPointerException: castToNonNull failed!
        at com.uber.nullaway.NullabilityUtil.castToNonNull(NullabilityUtil.java:409)
        at com.uber.nullaway.GenericsChecks.getGenericReturnNullnessAtInvocation(GenericsChecks.java:800)
        at com.uber.nullaway.dataflow.AccessPathNullnessPropagation.genericReturnIsNullable(AccessPathNullnessPropagation.java:1031)
        at com.uber.nullaway.dataflow.AccessPathNullnessPropagation.returnValueNullness(AccessPathNullnessPropagation.java:1008)
        at com.uber.nullaway.dataflow.AccessPathNullnessPropagation.visit
```
With the call to ```java ImmutableSet.of()``` which is a static call, we
were wrongly trying to return null from getTreeType in
GenericChecks.java for this case which caused the above Exception.

A unit test which reproduces the issue has been added to
NullAwayJSpecifyGenerickChecks.java:

```java
import org.jspecify.annotations.Nullable;
import com.google.common.collect.ImmutableSet;
class Test {
    static void funcImmutableSet(ImmutableSet<Object> is){
    }
    static void testNegative() {
		//We were getting the issue on this line
        funcImmutableSet(ImmutableSet.of());
    }
}
```

All the unit tests from the NullAway build have passed for these
changes.

---------

Co-authored-by: Manu Sridharan <[email protected]>

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

@@ -784,7 +784,7 @@ public static Nullness getGenericReturnNullnessAtInvocation(
       MethodInvocationTree tree,
       VisitorState state,
       Config config) {
-    if (!(tree.getMethodSelect() instanceof MemberSelectTree)) {
+    if (!(tree.getMethodSelect() instanceof MemberSelectTree) || invokedMethodSymbol.isStatic()) {
       return Nullness.NONNULL;
     }
     Type methodReceiverType =
@@ -834,7 +834,7 @@ public static Nullness getGenericParameterNullnessAtInvocation(
       MethodInvocationTree tree,
       VisitorState state,
       Config config) {
-    if (!(tree.getMethodSelect() instanceof MemberSelectTree)) {
+    if (!(tree.getMethodSelect() instanceof MemberSelectTree) || invokedMethodSymbol.isStatic()) {
       return Nullness.NONNULL;
     }
     Type enclosingType =

nullaway/src/test/java/com/uber/nullaway/NullAwayJSpecifyGenericsTests.java

@@ -1494,6 +1494,34 @@ public void interactionWithContracts() {
         .doTest();
   }
 
+  @Test
+  public void testForStaticMethodCallAsAParam() {
+    makeHelper()
+        .addSourceLines(
+            "Test.java",
+            "package com.uber;",
+            "import org.jspecify.annotations.Nullable;",
+            "class Test {",
+            "  static class A<T> {",
+            "   public static <T> A<T> returnA(){",
+            "     return new A<T>();",
+            "   }",
+            "   public static <T> A<T> returnAWithParam(Object o){",
+            "     return new A<T>();",
+            "   }",
+            "  }",
+            "  static void func(A<Object> a){",
+            "  }",
+            "  static void testNegative() {",
+            "   func(A.returnA());",
+            "  }",
+            "  static void testNegative2() {",
+            "   func(A.returnAWithParam(new Object()));",
+            "  }",
+            "}")
+        .doTest();
+  }
+
   private CompilationTestHelper makeHelper() {
     return makeTestHelperWithArgs(
         Arrays.asList(