diff --git a/.idea/workspace.xml b/.idea/workspace.xml
index 186519c..4e9c26f 100644
--- a/.idea/workspace.xml
+++ b/.idea/workspace.xml
@@ -4,9 +4,7 @@
     <option name="autoReloadType" value="SELECTIVE" />
   </component>
   <component name="ChangeListManager">
-    <list default="true" id="b3bac6d6-f8b1-474b-a5e1-72bf67a3867c" name="Changes" comment="add maven plugins to run junit5 test with maven">
-      <change beforePath="$PROJECT_DIR$/README.md" beforeDir="false" afterPath="$PROJECT_DIR$/README.md" afterDir="false" />
-    </list>
+    <list default="true" id="b3bac6d6-f8b1-474b-a5e1-72bf67a3867c" name="Changes" comment="add a badge, change name for the workflow" />
     <option name="SHOW_DIALOG" value="false" />
     <option name="HIGHLIGHT_CONFLICTS" value="true" />
     <option name="HIGHLIGHT_NON_ACTIVE_CHANGELIST" value="false" />
@@ -41,29 +39,29 @@
     <option name="hideEmptyMiddlePackages" value="true" />
     <option name="showLibraryContents" value="true" />
   </component>
-  <component name="PropertiesComponent"><![CDATA[{
-  "keyToString": {
-    "RunOnceActivity.OpenProjectViewOnStart": "true",
-    "RunOnceActivity.ShowReadmeOnStart": "true",
-    "SONARLINT_PRECOMMIT_ANALYSIS": "true",
-    "com.intellij.testIntegration.createTest.CreateTestDialog.defaultLibrary": "JUnit5",
-    "com.intellij.testIntegration.createTest.CreateTestDialog.defaultLibrarySuperClass.JUnit5": "",
-    "full.screen.before.presentation.mode": "false",
-    "last_opened_file_path": "C:/Users/divya/Exercism/java/need-for-speed",
-    "project.structure.last.edited": "Project",
-    "project.structure.proportion": "0.15",
-    "project.structure.side.proportion": "0.0",
-    "settings.editor.selected.configurable": "preferences.pluginManager"
+  <component name="PropertiesComponent">{
+  &quot;keyToString&quot;: {
+    &quot;RunOnceActivity.OpenProjectViewOnStart&quot;: &quot;true&quot;,
+    &quot;RunOnceActivity.ShowReadmeOnStart&quot;: &quot;true&quot;,
+    &quot;SONARLINT_PRECOMMIT_ANALYSIS&quot;: &quot;true&quot;,
+    &quot;com.intellij.testIntegration.createTest.CreateTestDialog.defaultLibrary&quot;: &quot;JUnit5&quot;,
+    &quot;com.intellij.testIntegration.createTest.CreateTestDialog.defaultLibrarySuperClass.JUnit5&quot;: &quot;&quot;,
+    &quot;full.screen.before.presentation.mode&quot;: &quot;false&quot;,
+    &quot;last_opened_file_path&quot;: &quot;C:/Users/divya/Exercism/java/need-for-speed&quot;,
+    &quot;project.structure.last.edited&quot;: &quot;Project&quot;,
+    &quot;project.structure.proportion&quot;: &quot;0.15&quot;,
+    &quot;project.structure.side.proportion&quot;: &quot;0.0&quot;,
+    &quot;settings.editor.selected.configurable&quot;: &quot;preferences.pluginManager&quot;
   },
-  "keyToStringList": {
-    "DatabaseDriversLRU": [
-      "mysql"
+  &quot;keyToStringList&quot;: {
+    &quot;DatabaseDriversLRU&quot;: [
+      &quot;mysql&quot;
     ],
-    "com.intellij.ide.scratch.ScratchImplUtil$2/New Scratch File": [
-      "Markdown"
+    &quot;com.intellij.ide.scratch.ScratchImplUtil$2/New Scratch File&quot;: [
+      &quot;Markdown&quot;
     ]
   }
-}]]></component>
+}</component>
   <component name="RecentsManager">
     <key name="CreateTestDialog.Recents.Supers">
       <recent name="" />
@@ -166,7 +164,7 @@
       <workItem from="1652622259082" duration="160000" />
       <workItem from="1652631231540" duration="1640000" />
       <workItem from="1652638374278" duration="312000" />
-      <workItem from="1652815591071" duration="2395000" />
+      <workItem from="1652815591071" duration="2935000" />
     </task>
     <task id="LOCAL-00001" summary="initial commit">
       <created>1652464516513</created>
@@ -301,7 +299,14 @@
       <option name="project" value="LOCAL" />
       <updated>1652819174296</updated>
     </task>
-    <option name="localTasksCounter" value="20" />
+    <task id="LOCAL-00020" summary="add a badge, change name for the workflow">
+      <created>1652819472258</created>
+      <option name="number" value="00020" />
+      <option name="presentableId" value="LOCAL-00020" />
+      <option name="project" value="LOCAL" />
+      <updated>1652819472258</updated>
+    </task>
+    <option name="localTasksCounter" value="21" />
     <servers />
   </component>
   <component name="Vcs.Log.Tabs.Properties">
@@ -336,7 +341,8 @@
     <MESSAGE value="add proper test names" />
     <MESSAGE value="change maven target version to 11" />
     <MESSAGE value="add maven plugins to run junit5 test with maven" />
-    <option name="LAST_COMMIT_MESSAGE" value="add maven plugins to run junit5 test with maven" />
+    <MESSAGE value="add a badge, change name for the workflow" />
+    <option name="LAST_COMMIT_MESSAGE" value="add a badge, change name for the workflow" />
     <option name="OPTIMIZE_IMPORTS_BEFORE_PROJECT_COMMIT" value="true" />
     <option name="REFORMAT_BEFORE_PROJECT_COMMIT" value="true" />
     <option name="REARRANGE_BEFORE_PROJECT_COMMIT" value="true" />
diff --git a/README.md b/README.md
index 0b7ed94..454aed7 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-[![Test Case Report](https://github.com/dbc2201/JavaCodingProblem1/actions/workflows/maven.yml/badge.svg?event=push)](https://github.com/dbc2201/JavaCodingProblem1/actions/workflows/maven.yml) [![Lint Code Base](https://github.com/dbc2201/JavaCodingProblem1/actions/workflows/super-linter.yml/badge.svg)](https://github.com/dbc2201/JavaCodingProblem1/actions/workflows/super-linter.yml)
+[![Test Case Report](https://github.com/dbc2201/JavaCodingProblem1/actions/workflows/maven.yml/badge.svg?event=push)](https://github.com/dbc2201/JavaCodingProblem1/actions/workflows/maven.yml) 
 # Java Coding Problems
 
 ## Chapter 1: Strings, Numbers, and Math
diff --git a/src/main/java/io/github/dbc/DuplicateCharactersCounter.java b/src/main/java/io/github/dbc/DuplicateCharactersCounter.java
index 9020649..49cee5a 100644
--- a/src/main/java/io/github/dbc/DuplicateCharactersCounter.java
+++ b/src/main/java/io/github/dbc/DuplicateCharactersCounter.java
@@ -8,6 +8,7 @@ public class DuplicateCharactersCounter {
      *
      * @param string String to count duplicate characters.
      * @return Map with characters and their count.
+     * @throws IllegalArgumentException if the input is null or empty.
      */
     public Map<Character, Integer> countDuplicateCharacters(String string) {
         return Map.of();