Updated name validation

src/main/java/com/zipcodewilmington/phonebook/PhoneBook.java

@@ -37,8 +37,13 @@ public class PhoneBook {
 
 
     public String lookupByName(String lookupName) {
+        for (String key: allNames) {
+            if (key.equals(lookupName)) {
+                return this.phoneList.get(lookupName).toString();
+            }
+        }
 
-        return this.phoneList.get(lookupName).toString();
+        return "Invalid Name.";
     }
 
     public void removeRecord(String nameToRemove) {