Fix crash of nearby list when the places list is null

Currently the NearbyController crashes when it is called with a
places list that is null. This is caused by the NearbyMapFragment
not handling this state correctly.
This commit adds tests for an empty list and null, which reproduce
the problem. An early return in the NearbyController can make
the tests pass, but might not be the best solution for this issue.

app/src/androidTest/java/fr/free/nrw/commons/NearbyControllerTest.java

@@ -0,0 +1,57 @@
+package fr.free.nrw.commons;
+
+import android.content.Context;
+import android.support.test.InstrumentationRegistry;
+import android.support.test.runner.AndroidJUnit4;
+
+import fr.free.nrw.commons.location.LatLng;
+import fr.free.nrw.commons.nearby.NearbyBaseMarker;
+import fr.free.nrw.commons.nearby.NearbyController;
+import fr.free.nrw.commons.nearby.Place;
+
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.hamcrest.CoreMatchers.is;
+
+@RunWith(AndroidJUnit4.class)
+public class NearbyControllerTest {
+    private Context instrumentationContext;
+
+    @Before
+    public void setup() {
+        instrumentationContext = InstrumentationRegistry.getContext();
+    }
+
+    @Test public void testNullAttractions() {
+        LatLng location = new LatLng(0, 0);
+
+        List<NearbyBaseMarker> options =
+            NearbyController.loadAttractionsFromLocationToBaseMarkerOptions(
+                location,
+                null,
+                instrumentationContext
+        );
+
+        Assert.assertThat(options.size(), is(0));
+    }
+
+    @Test public void testEmptyList() {
+        LatLng location = new LatLng(0, 0);
+        List<Place> emptyList = new ArrayList<>();
+
+        List<NearbyBaseMarker> options =
+                NearbyController.loadAttractionsFromLocationToBaseMarkerOptions(
+                        location,
+                        emptyList,
+                        instrumentationContext
+                );
+
+        Assert.assertThat(options.size(), is(0));
+    }
+}