ATLAS-1663: Fix defects reported by Coverity Scan

graphdb/titan0/src/main/java/org/apache/atlas/repository/graphdb/titan0/Titan0Graph.java

@@ -290,7 +290,9 @@ public class Titan0Graph implements AtlasGraph<Titan0Vertex, Titan0Edge> {
         ScriptEngine        engine  = manager.getEngineByName("gremlin-groovy");
 
         //Do not cache script compilations due to memory implications
+        if (engine != null) {
             engine.getContext().setAttribute("#jsr223.groovy.engine.keep.globals", "phantom", ScriptContext.ENGINE_SCOPE);
+        }
 
         return engine;
     }

webapp/src/main/java/org/apache/atlas/web/rest/EntityREST.java

@@ -424,7 +424,7 @@ public class EntityREST {
         try {
             if (AtlasPerfTracer.isPerfTraceEnabled(PERF_LOG)) {
                 perf = AtlasPerfTracer.getPerfTracer(PERF_LOG, "EntityREST.createOrUpdate(entityCount=" +
-                                                               (entities == null || entities.getEntities() == null ? 0 : entities.getEntities().size()) + ")");
+                                                               (CollectionUtils.isEmpty(entities.getEntities()) ? 0 : entities.getEntities().size()) + ")");
             }
 
             EntityStream entityStream = new AtlasEntityStream(entities);