Use map.computeIfAbsent

Java 8 simplifies adding a value to a key in a map using a function.

Change-Id: Icb9632960d4c1c91bf6f9504cb6df78da757dfba
diff --git a/src/main/java/com/googlesource/gerrit/plugins/its/base/util/IssueExtractor.java b/src/main/java/com/googlesource/gerrit/plugins/its/base/util/IssueExtractor.java
index d367cb0..75a1cc3 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/its/base/util/IssueExtractor.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/its/base/util/IssueExtractor.java
@@ -57,7 +57,7 @@
   }
 
   /**
-   * Helper funcion for {@link #getIssueIds(String, String)}.
+   * Helper function for {@link #getIssueIds(String, String)}.
    *
    * <p>Adds a text's issues for a given occurrence to the map returned by {@link
    * #getIssueIds(String, String)}.
@@ -68,11 +68,7 @@
    */
   private void addIssuesOccurrence(String text, String occurrence, Map<String, Set<String>> map) {
     for (String issue : getIssueIds(text)) {
-      Set<String> occurrences = map.get(issue);
-      if (occurrences == null) {
-        occurrences = Sets.newLinkedHashSet();
-        map.put(issue, occurrences);
-      }
+      Set<String> occurrences = map.computeIfAbsent(issue, k -> Sets.newLinkedHashSet());
       occurrences.add(occurrence);
     }
   }