Workaround NullAway bug on AssertJ null-check

It seems assertThat(obj).isNotNull(); does not qualify as a null-check
for NullAway if obj is a collection.

See uber/NullAway#1219

Author: jonatan-ivanov

micrometer-core/src/test/java/io/micrometer/core/instrument/push/PushMeterRegistryTest.java

@@ -127,7 +127,9 @@ void doNotPublishAgainOnClose_whenScheduledPublishInProgress() throws Interrupte
         onClosePublishThread.join();
 
         assertThat(overlappingStepMeterRegistry.publishes).as("only one publish happened").hasSize(1);
-        Deque<Double> firstPublishValues = overlappingStepMeterRegistry.publishes.get(0);
+        // TODO: remove requireNonNull: https://github.com/uber/NullAway/issues/1219
+        Deque<Double> firstPublishValues = Objects.requireNonNull(overlappingStepMeterRegistry.publishes.get(0));
+        assertThat(firstPublishValues).isNotNull();
         assertThat(firstPublishValues.pop()).isEqualTo(1);
         assertThat(firstPublishValues.pop()).isEqualTo(2.5);
     }
@@ -189,7 +191,9 @@ void waitForScheduledPublishToFinish_whenClosedWhilePublishIsInProgress()
         closeThread.join();
 
         assertThat(registry.publishes).as("only one publish happened").hasSize(1);
-        Deque<Double> firstPublishValues = registry.publishes.get(0);
+        // TODO: remove requireNonNull: https://github.com/uber/NullAway/issues/1219
+        Deque<Double> firstPublishValues = Objects.requireNonNull(registry.publishes.get(0));
+        assertThat(firstPublishValues).isNotNull();
         assertThat(firstPublishValues.pop()).isEqualTo(1); // c1 counter count
         assertThat(firstPublishValues.pop()).isEqualTo(2.5); // c2 counter count
     }