Add more informative errors for null ElementCache

Author: labkey-tchad

src/org/labkey/test/components/Component.java

@@ -27,6 +27,7 @@
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.function.Function;
 
@@ -69,8 +70,9 @@ protected EC elementCache()
                 // Pass if element doesn't exist. Might be checking if component is visible.
             }
 
-            _elementCache = newElementCache();
+            _elementCache = Objects.requireNonNull(newElementCache());
             waitForReady();
+            Objects.requireNonNull(_elementCache, "waitForReady() cleared the element cache");
         }
         return _elementCache;
     }