NotNull

platform/vcs-api/src/com/intellij/openapi/vcs/merge/MergeProvider2.java

@@ -36,6 +36,6 @@ public interface MergeProvider2 extends MergeProvider {
    * @return the merge session instance.
    */
   @NotNull
-  MergeSession createMergeSession(List<VirtualFile> files);
+  MergeSession createMergeSession(@NotNull List<VirtualFile> files);
 
 }

platform/vcs-api/src/com/intellij/openapi/vcs/merge/MergeSession.java

@@ -17,6 +17,7 @@ package com.intellij.openapi.vcs.merge;
 
 import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.util.ui.ColumnInfo;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * Represents the state of a multiple file merge operation.
@@ -36,6 +37,7 @@ public interface MergeSession {
    *
    * @return the list of columns, or an empty list if no additional columns should be displayed.
    */
+  @NotNull
   ColumnInfo[] getMergeInfoColumns();
 
   /**
@@ -44,7 +46,7 @@ public interface MergeSession {
    * @param file a file shown in the dialog.
    * @return true if the merge dialog can be shown, false otherwise.
    */
-  boolean canMerge(VirtualFile file);
+  boolean canMerge(@NotNull VirtualFile file);
 
   /**
    * Called when the user executes one of the resolve actions (merge, accept yours, accept theirs) for
@@ -54,6 +56,6 @@ public interface MergeSession {
    * @param file       the conflicting file.
    * @param resolution the used resolution.
    */
-  void conflictResolvedForFile(VirtualFile file, Resolution resolution);
+  void conflictResolvedForFile(@NotNull VirtualFile file, @NotNull Resolution resolution);
 
 }

plugins/git4idea/src/git4idea/merge/GitMergeProvider.java

@@ -223,7 +223,7 @@ public class GitMergeProvider implements MergeProvider2 {
 
   @Override
   @NotNull
-  public MergeSession createMergeSession(List<VirtualFile> files) {
+  public MergeSession createMergeSession(@NotNull List<VirtualFile> files) {
     return new MyMergeSession(files);
   }
 
@@ -309,19 +309,20 @@ public class GitMergeProvider implements MergeProvider2 {
       }
     }
 
+    @NotNull
     @Override
     public ColumnInfo[] getMergeInfoColumns() {
       return new ColumnInfo[]{new StatusColumn(false), new StatusColumn(true)};
     }
 
     @Override
-    public boolean canMerge(VirtualFile file) {
+    public boolean canMerge(@NotNull VirtualFile file) {
       Conflict c = myConflicts.get(file);
       return c != null;
     }
 
     @Override
-    public void conflictResolvedForFile(VirtualFile file, Resolution resolution) {
+    public void conflictResolvedForFile(VirtualFile file, @NotNull Resolution resolution) {
       Conflict c = myConflicts.get(file);
       assert c != null : "Conflict was not loaded for the file: " + file.getPath();
       try {