Map.getOrDefault/putIfAbsent/merge used where safe; warnings fixed

java/idea-ui/src/com/intellij/facet/impl/ui/libraries/LibraryDownloadSettings.java

@@ -148,7 +148,7 @@ public class LibraryDownloadSettings {
     }
     libraryEditor.setName(myLibraryName);
     for (Pair<VirtualFile, DownloadableFileDescription> pair : downloaded) {
-      final OrderRootType rootType = rootTypes.containsKey(pair.getSecond()) ? rootTypes.get(pair.getSecond()) : OrderRootType.CLASSES;
+      final OrderRootType rootType = rootTypes.getOrDefault(pair.getSecond(), OrderRootType.CLASSES);
       libraryEditor.addRoot(pair.getFirst(), rootType);
     }
     return libraryEditor;

java/java-psi-impl/src/com/intellij/psi/impl/JavaPsiFacadeImpl.java

@@ -361,9 +361,7 @@ public class JavaPsiFacadeImpl extends JavaPsiFacadeEx {
       // (the Kotlin plugin can do that), the Java package takes precedence.
       PsiPackage[] packages = finder.getSubPackages(psiPackage, scope);
       for (PsiPackage aPackage : packages) {
-        if (result.get(aPackage.getName()) == null) {
-          result.put(aPackage.getName(), aPackage);
-        }
+        result.putIfAbsent(aPackage.getName(), aPackage);
       }
     }
     return result.values().toArray(PsiPackage.EMPTY_ARRAY);

platform/lang-impl/src/com/intellij/application/options/codeStyle/OptionTreeWithPreviewPanel.java

@@ -642,6 +642,6 @@ public abstract class OptionTreeWithPreviewPanel extends CustomizableLanguageCod
   }
 
   private String getRemappedGroup(String fieldName, String defaultName) {
-    return myRemappedGroups.containsKey(fieldName) ? myRemappedGroups.get(fieldName) : defaultName;
+    return myRemappedGroups.getOrDefault(fieldName, defaultName);
   }
 }

platform/lang-impl/src/com/intellij/slicer/DuplicateMap.java

@@ -46,11 +46,7 @@ public class DuplicateMap {
   SliceNode putNodeCheckDupe(@NotNull final SliceNode node) {
     return ReadAction.compute(() -> {
       SliceUsage usage = node.getValue();
-      SliceNode eq = myDuplicates.get(usage);
-      if (eq == null) {
-        myDuplicates.put(usage, node);
-      }
-      return eq;
+      return myDuplicates.putIfAbsent(usage, node);
     });
   }