PY-18039 PyPackageManager#getDependents() returns @NotNull value

python/openapi/src/com/jetbrains/python/packaging/PyPackageManager.java

@@ -62,6 +62,6 @@ public abstract class PyPackageManager {
   @Nullable
   public abstract List<PyRequirement> getRequirements(@NotNull Module module);
 
-  @Nullable
+  @NotNull
   public abstract Set<PyPackage> getDependents(@NotNull PyPackage pkg) throws ExecutionException;
 }

python/src/com/jetbrains/python/packaging/PyPackageManagerImpl.java

@@ -278,7 +278,7 @@ public class PyPackageManagerImpl extends PyPackageManager {
   }
 
   @Override
-  @Nullable
+  @NotNull
   public Set<PyPackage> getDependents(@NotNull PyPackage pkg) throws ExecutionException {
     final List<PyPackage> packages = refreshAndGetPackages(false);
     final Set<PyPackage> dependents = new HashSet<>();

python/src/com/jetbrains/python/packaging/PyPackageManagersImpl.java

@@ -148,7 +148,7 @@ public class PyPackageManagersImpl extends PyPackageManagers {
       return null;
     }
 
-    @Nullable
+    @NotNull
     @Override
     public Set<PyPackage> getDependents(@NotNull PyPackage pkg) throws ExecutionException {
       throw new ExecutionException(getErrorMessage());