diff --git a/platform/platform-api/src/com/intellij/openapi/diff/MergeRequest.java b/platform/platform-api/src/com/intellij/openapi/diff/MergeRequest.java
index 29243f7b9be0..ce8d56044f96 100644
--- a/platform/platform-api/src/com/intellij/openapi/diff/MergeRequest.java
+++ b/platform/platform-api/src/com/intellij/openapi/diff/MergeRequest.java
@@ -25,7 +25,7 @@ import org.jetbrains.annotations.Nullable;
  * @see DiffRequestFactory#createMergeRequest
  */
 public abstract class MergeRequest extends DiffRequest {
-  protected MergeRequest(Project project) {
+  protected MergeRequest(@Nullable Project project) {
     super(project);
   }
 
diff --git a/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/DiffRequestFactoryImpl.java b/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/DiffRequestFactoryImpl.java
index 221a082d5367..962a0712465b 100644
--- a/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/DiffRequestFactoryImpl.java
+++ b/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/DiffRequestFactoryImpl.java
@@ -28,11 +28,11 @@ import org.jetbrains.annotations.Nullable;
 
 public class DiffRequestFactoryImpl extends DiffRequestFactory {
 
-  public MergeRequest createMergeRequest(String leftText,
-                                         String rightText,
-                                         String originalContent,
+  public MergeRequest createMergeRequest(@NotNull String leftText,
+                                         @NotNull String rightText,
+                                         @NotNull String originalContent,
                                          @NotNull VirtualFile file,
-                                         Project project,
+                                         @Nullable Project project,
                                          @Nullable final ActionButtonPresentation okButtonPresentation,
                                          @Nullable final ActionButtonPresentation cancelButtonPresentation) {
     final Document document = FileDocumentManager.getInstance().getDocument(file);
@@ -46,23 +46,20 @@ public class DiffRequestFactoryImpl extends DiffRequestFactory {
     }
   }
 
-  public MergeRequest create3WayDiffRequest(final String leftText,
-                                            final String rightText,
-                                            final String originalContent,
+  public MergeRequest create3WayDiffRequest(@NotNull String leftText,
+                                            @NotNull String rightText,
+                                            @NotNull String originalContent,
                                             @Nullable FileType type,
-                                            final Project project,
+                                            @Nullable Project project,
                                             @Nullable final ActionButtonPresentation okButtonPresentation,
                                             @Nullable final ActionButtonPresentation cancelButtonPresentation) {
-    if (type != null) {
-      return new MergeRequestImpl(leftText, originalContent, rightText, type, project, okButtonPresentation, cancelButtonPresentation);
-    }
-    return new MergeRequestImpl(leftText, originalContent, rightText, project, okButtonPresentation, cancelButtonPresentation);
+    return new MergeRequestImpl(leftText, originalContent, rightText, type, project, okButtonPresentation, cancelButtonPresentation);
   }
 
-  public MergeRequest create3WayDiffRequest(final String leftText,
-                                            final String rightText,
-                                            final String originalContent,
-                                            final Project project,
+  public MergeRequest create3WayDiffRequest(@NotNull String leftText,
+                                            @NotNull String rightText,
+                                            @NotNull String originalContent,
+                                            @Nullable Project project,
                                             @Nullable final ActionButtonPresentation okButtonPresentation,
                                             @Nullable final ActionButtonPresentation cancelButtonPresentation) {
     return create3WayDiffRequest(leftText, rightText, originalContent, null, project, okButtonPresentation, cancelButtonPresentation);
diff --git a/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeRequestImpl.java b/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeRequestImpl.java
index f6642b720acc..938c1ee7a42d 100644
--- a/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeRequestImpl.java
+++ b/platform/platform-impl/src/com/intellij/openapi/diff/impl/mergeTool/MergeRequestImpl.java
@@ -47,40 +47,39 @@ public class MergeRequestImpl extends MergeRequest {
   @Nullable private final ActionButtonPresentation myOkButtonPresentation;
   @Nullable private final ActionButtonPresentation myCancelButtonPresentation;
 
-  public MergeRequestImpl(String left,
-                          MergeVersion base,
-                          String right,
-                          Project project,
+  public MergeRequestImpl(@NotNull String left,
+                          @NotNull MergeVersion base,
+                          @NotNull String right,
+                          @Nullable Project project,
                           @Nullable final ActionButtonPresentation okButtonPresentation,
                           @Nullable final ActionButtonPresentation cancelButtonPresentation) {
     this(new SimpleContent(left), new MergeContent(base, project), new SimpleContent(right), project, okButtonPresentation,
          cancelButtonPresentation);
   }
 
-  public MergeRequestImpl(DiffContent left,
-                          MergeVersion base,
-                          DiffContent right,
-                          Project project,
+  public MergeRequestImpl(@NotNull DiffContent left,
+                          @NotNull MergeVersion base,
+                          @NotNull DiffContent right,
+                          @Nullable Project project,
                           @Nullable final ActionButtonPresentation okButtonPresentation,
                           @Nullable final ActionButtonPresentation cancelButtonPresentation) {
     this(left, new MergeContent(base, project), right, project, okButtonPresentation, cancelButtonPresentation);
   }
 
-  public MergeRequestImpl(String left,
-                          String base,
-                          String right,
-                          Project project,
+  public MergeRequestImpl(@NotNull String left,
+                          @NotNull String base,
+                          @NotNull String right,
+                          @Nullable Project project,
                           @Nullable final ActionButtonPresentation okButtonPresentation,
                           @Nullable final ActionButtonPresentation cancelButtonPresentation) {
-    this(new SimpleContent(left), new SimpleContent(base), new SimpleContent(right), project, okButtonPresentation,
-         cancelButtonPresentation);
+    this(left, base, right, null, project, okButtonPresentation, cancelButtonPresentation);
   }
 
-  public MergeRequestImpl(String left,
-                          String base,
-                          String right,
-                          FileType type,
-                          Project project,
+  public MergeRequestImpl(@NotNull String left,
+                          @NotNull String base,
+                          @NotNull String right,
+                          @Nullable FileType type,
+                          @Nullable Project project,
                           @Nullable final ActionButtonPresentation okButtonPresentation,
                           @Nullable final ActionButtonPresentation cancelButtonPresentation) {
     this(new SimpleContent(left, type),
@@ -89,10 +88,10 @@ public class MergeRequestImpl extends MergeRequest {
          project, okButtonPresentation, cancelButtonPresentation);
   }
 
-  private MergeRequestImpl(DiffContent left,
-                           DiffContent base,
-                           DiffContent right,
-                           Project project,
+  private MergeRequestImpl(@NotNull DiffContent left,
+                           @NotNull DiffContent base,
+                           @NotNull DiffContent right,
+                           @Nullable Project project,
                            @Nullable final ActionButtonPresentation okButtonPresentation,
                            @Nullable final ActionButtonPresentation cancelButtonPresentation) {
     super(project);
@@ -240,11 +239,11 @@ public class MergeRequestImpl extends MergeRequest {
   }
 
   public static class MergeContent extends DiffContent {
-    private final MergeVersion myTarget;
+    @NotNull private final MergeVersion myTarget;
     private final Document myWorkingDocument;
     private final Project myProject;
 
-    public MergeContent(MergeVersion target, Project project) {
+    public MergeContent(@NotNull MergeVersion target, Project project) {
       myTarget = target;
       myProject = project;
       myWorkingDocument = myTarget.createWorkingDocument(project);