add isEmpty to TypesDef and check in MetadataService

repository/src/main/java/org/apache/hadoop/metadata/services/DefaultMetadataService.java

@@ -94,7 +94,7 @@ public class DefaultMetadataService implements MetadataService {
             Preconditions.checkArgument(!typeDefinition.equals(""), "type definition cannot be an empty string");
 
             TypesDef typesDef = TypesSerialization.fromJson(typeDefinition);
-            if(typesDef.classTypesAsJavaList().size() == 0)
+            if(typesDef.isEmpty())
                 throw new MetadataException("Invalid type definition");
 
             Map<String, IDataType> typesAdded = typeSystem.defineTypes(typesDef);

typesystem/src/main/scala/org/apache/hadoop/metadata/typesystem/TypesDef.scala

@@ -58,4 +58,8 @@ case class TypesDef(enumTypes: Seq[EnumTypeDefinition],
         import scala.collection.JavaConverters._
         classTypes.asJava
     }
+
+    def isEmpty() = {
+      enumTypes.isEmpty & structTypes.isEmpty & traitTypes.isEmpty & classTypes.isEmpty
+    }
 }