fix: Add missing docs

markdown/src/main/java/org/apache/zeppelin/markdown/ParamVar.java

@@ -22,6 +22,9 @@ import org.parboiled.support.Var;
 import java.util.HashMap;
 import java.util.Map;
 
+/**
+ * Implementation of Var to support parameter parsing
+ */
 public class ParamVar<K, V> extends Var<Map<K, V>> {
 
   public ParamVar() {

markdown/src/main/java/org/apache/zeppelin/markdown/PegdownWebSequencelPlugin.java

@@ -37,6 +37,9 @@ import java.net.URLConnection;
 import java.net.URLEncoder;
 import java.nio.charset.StandardCharsets;
 
+/**
+ * Pegdown plugin for Websequence diagram
+ */
 public class PegdownWebSequencelPlugin extends Parser implements BlockPluginParser {
 
   public PegdownWebSequencelPlugin() {

markdown/src/main/java/org/apache/zeppelin/markdown/PegdownYumlPlugin.java

@@ -32,6 +32,9 @@ import java.io.UnsupportedEncodingException;
 import java.net.URLEncoder;
 import java.util.Map;
 
+/**
+ * Pegdown plugin for YUML
+ */
 public class PegdownYumlPlugin extends Parser implements BlockPluginParser {
 
   public PegdownYumlPlugin() {

markdown/src/test/java/org/apache/zeppelin/markdown/PegdownParserTest.java

@@ -317,7 +317,6 @@ public class PegdownParserTest {
         .toString();
 
     InterpreterResult result = md.interpret(input, null);
-    assertEquals("", result.message());
     assertThat(result.message(), CoreMatchers.containsString("<img src=\"http://www.websequencediagrams.com/?png="));
   }