diff --git a/platform/core-impl/src/com/intellij/extapi/psi/ASTDelegatePsiElement.java b/platform/core-impl/src/com/intellij/extapi/psi/ASTDelegatePsiElement.java
index bedda72b6ae4..aa080677a16e 100644
--- a/platform/core-impl/src/com/intellij/extapi/psi/ASTDelegatePsiElement.java
+++ b/platform/core-impl/src/com/intellij/extapi/psi/ASTDelegatePsiElement.java
@@ -166,12 +166,12 @@ public abstract class ASTDelegatePsiElement extends PsiElementBase {
     return getNode().getElementType().getLanguage();
   }
 
-  protected @Nullable <T extends PsiElement> T findChildByType(IElementType type) {
+  protected @Nullable <T extends PsiElement> T findChildByType(@NotNull IElementType type) {
     ASTNode node = getNode().findChildByType(type);
     return node == null ? null : (T)node.getPsi();
   }
 
-  protected @Nullable <T extends PsiElement> T findLastChildByType(IElementType type) {
+  protected @Nullable <T extends PsiElement> T findLastChildByType(@NotNull IElementType type) {
     PsiElement child = getLastChild();
     while (child != null) {
       final ASTNode node = child.getNode();
@@ -181,18 +181,16 @@ public abstract class ASTDelegatePsiElement extends PsiElementBase {
     return null;
   }
 
-
-
-  protected @NotNull <T extends PsiElement> T findNotNullChildByType(IElementType type) {
+  protected @NotNull <T extends PsiElement> T findNotNullChildByType(@NotNull IElementType type) {
     return notNullChild(findChildByType(type));
   }
 
-  protected @Nullable <T extends PsiElement> T findChildByType(TokenSet type) {
+  protected @Nullable <T extends PsiElement> T findChildByType(@NotNull TokenSet type) {
     ASTNode node = getNode().findChildByType(type);
     return node == null ? null : (T)node.getPsi();
   }
 
-  protected @NotNull <T extends PsiElement> T findNotNullChildByType(TokenSet type) {
+  protected @NotNull <T extends PsiElement> T findNotNullChildByType(@NotNull TokenSet type) {
     return notNullChild(findChildByType(type));
   }
 
@@ -200,16 +198,16 @@ public abstract class ASTDelegatePsiElement extends PsiElementBase {
    * @deprecated Use {@link #findChildByType(TokenSet)} instead
    */
   @Deprecated
-  protected @Nullable PsiElement findChildByFilter(TokenSet tokenSet) {
+  protected @Nullable PsiElement findChildByFilter(@NotNull TokenSet tokenSet) {
     ASTNode[] nodes = getNode().getChildren(tokenSet);
     return nodes.length == 0 ? null : nodes[0].getPsi();
   }
 
-  protected <T extends PsiElement> T @NotNull [] findChildrenByType(IElementType elementType, Class<T> arrayClass) {
+  protected <T extends PsiElement> T @NotNull [] findChildrenByType(@NotNull IElementType elementType, @NotNull Class<T> arrayClass) {
     return ContainerUtil.map2Array(SharedImplUtil.getChildrenOfType(getNode(), elementType), arrayClass, s -> (T)s.getPsi());
   }
 
-  protected @Unmodifiable <T extends PsiElement> List<T> findChildrenByType(@NotNull TokenSet elementType) {
+  protected @Unmodifiable <T extends PsiElement> @NotNull List<T> findChildrenByType(@NotNull TokenSet elementType) {
     List<T> result = Collections.emptyList();
     ASTNode child = getNode().getFirstChildNode();
     while (child != null) {
@@ -225,7 +223,7 @@ public abstract class ASTDelegatePsiElement extends PsiElementBase {
     return result;
   }
 
-  protected @Unmodifiable <T extends PsiElement> List<T> findChildrenByType(@NotNull IElementType elementType) {
+  protected @Unmodifiable <T extends PsiElement> @NotNull List<T> findChildrenByType(@NotNull IElementType elementType) {
     List<T> result = Collections.emptyList();
     ASTNode child = getNode().getFirstChildNode();
     while (child != null) {
@@ -259,7 +257,7 @@ public abstract class ASTDelegatePsiElement extends PsiElementBase {
     return addInnerBefore(element, anchor);
   }
 
-  private PsiElement addInnerBefore(final PsiElement element, final PsiElement anchor) throws IncorrectOperationException {
+  private PsiElement addInnerBefore(@NotNull PsiElement element, @Nullable PsiElement anchor) throws IncorrectOperationException {
     CheckUtil.checkWritable(this);
     TreeElement elementCopy = ChangeUtil.copyToElement(element);
     ASTNode treeElement = addInternal(elementCopy, elementCopy, SourceTreeToPsiMap.psiElementToTree(anchor), Boolean.TRUE);
@@ -288,7 +286,7 @@ public abstract class ASTDelegatePsiElement extends PsiElementBase {
     CheckUtil.checkWritable(this);
   }
 
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, @Nullable ASTNode anchor, @Nullable Boolean before) {
     return CodeEditUtil.addChildren(getNode(), first, last, getAnchorNode(anchor, before));
   }
 
@@ -371,20 +369,18 @@ public abstract class ASTDelegatePsiElement extends PsiElementBase {
     CodeEditUtil.replaceChild(getNode(), child.getNode(), newElement);
   }
 
-  private ASTNode getAnchorNode(final ASTNode anchor, final Boolean before) {
-    ASTNode anchorBefore;
+  private @Nullable ASTNode getAnchorNode(@Nullable ASTNode anchor, @Nullable Boolean before) {
+    assert (anchor == null) || (anchor != null && before != null);
+
     if (anchor != null) {
-      anchorBefore = before.booleanValue() ? anchor : anchor.getTreeNext();
+      return before.booleanValue() ? anchor : anchor.getTreeNext();
+    }
+    else if (before != null && !before.booleanValue()) {
+      return getNode().getFirstChildNode();
     }
     else {
-      if (before != null && !before.booleanValue()) {
-        anchorBefore = getNode().getFirstChildNode();
-      }
-      else {
-        anchorBefore = null;
-      }
+      return null;
     }
-    return anchorBefore;
   }
 
   @Override
diff --git a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/GrListOrMapImpl.java b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/GrListOrMapImpl.java
index fdcc50501b74..40f1096280f0 100644
--- a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/GrListOrMapImpl.java
+++ b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/GrListOrMapImpl.java
@@ -1,4 +1,4 @@
-// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package org.jetbrains.plugins.groovy.lang.psi.impl.auxiliary;
 
 import com.intellij.lang.ASTNode;
@@ -47,7 +47,7 @@ public class GrListOrMapImpl extends GrExpressionImpl implements GrListOrMap, Ps
   }
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean before) {
     if (getInitializers().length == 0) {
       return super.addInternal(first, last, getNode().getFirstChildNode(), false);
     }
diff --git a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/annotation/GrAnnotationArgumentListImpl.java b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/annotation/GrAnnotationArgumentListImpl.java
index 9517664da273..45a43646b13e 100644
--- a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/annotation/GrAnnotationArgumentListImpl.java
+++ b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/annotation/GrAnnotationArgumentListImpl.java
@@ -1,4 +1,4 @@
-// Copyright 2000-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package org.jetbrains.plugins.groovy.lang.psi.impl.auxiliary.annotation;
 
 import com.intellij.lang.ASTNode;
@@ -51,7 +51,7 @@ public class GrAnnotationArgumentListImpl extends GrStubElementBase<EmptyStub>
   }
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean before) {
     if (first.getElementType() == GroovyStubElementTypes.ANNOTATION_MEMBER_VALUE_PAIR && last.getElementType() ==
                                                                                          GroovyStubElementTypes.ANNOTATION_MEMBER_VALUE_PAIR) {
       ASTNode lparenth = getNode().getFirstChildNode();
diff --git a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/annotation/GrAnnotationArrayInitializerImpl.java b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/annotation/GrAnnotationArrayInitializerImpl.java
index ae6ab0c2056a..eea09b54fb5a 100644
--- a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/annotation/GrAnnotationArrayInitializerImpl.java
+++ b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/annotation/GrAnnotationArrayInitializerImpl.java
@@ -1,4 +1,4 @@
-// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package org.jetbrains.plugins.groovy.lang.psi.impl.auxiliary.annotation;
 
 import com.intellij.lang.ASTNode;
@@ -44,7 +44,7 @@ public class GrAnnotationArrayInitializerImpl extends GroovyPsiElementImpl imple
   }
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean before) {
     final GrAnnotationMemberValue[] initializers = getInitializers();
     if (initializers.length == 0) {
       return super.addInternal(first, last, getNode().getFirstChildNode(), false);
diff --git a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/modifiers/GrModifierListImpl.java b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/modifiers/GrModifierListImpl.java
index 0941b1da8e25..3df706f74ea4 100644
--- a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/modifiers/GrModifierListImpl.java
+++ b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/auxiliary/modifiers/GrModifierListImpl.java
@@ -1,4 +1,4 @@
-// Copyright 2000-2022 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package org.jetbrains.plugins.groovy.lang.psi.impl.auxiliary.modifiers;
 
 import com.intellij.lang.ASTNode;
@@ -232,7 +232,7 @@ public final class GrModifierListImpl extends GrStubElementBase<GrModifierListSt
   }
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean before) {
     final ASTNode node = super.addInternal(first, last, anchor, before);
     final PsiElement sibling = getNextSibling();
     if (sibling != null && sibling.getText().contains("\n")) {
diff --git a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/params/GrParameterListImpl.java b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/params/GrParameterListImpl.java
index 77966f88d9c6..6e7b3bf3c98d 100644
--- a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/params/GrParameterListImpl.java
+++ b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/params/GrParameterListImpl.java
@@ -1,4 +1,4 @@
-// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package org.jetbrains.plugins.groovy.lang.psi.impl.statements.params;
 
 import com.intellij.lang.ASTNode;
@@ -145,7 +145,7 @@ public class GrParameterListImpl extends GrStubElementBase<EmptyStub>
 
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean before) {
     GrParameter[] params = getParameters();
     ASTNode result = super.addInternal(first, last, anchor == null ? findChildByType(before ? T_RPAREN : T_LPAREN) : anchor, before);
     if (first == last && first.getPsi() instanceof GrParameter && params.length > 0) {
diff --git a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/typedef/GrTypeDefinitionBodyBase.java b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/typedef/GrTypeDefinitionBodyBase.java
index f5c9922fe164..00d362cd1f8c 100644
--- a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/typedef/GrTypeDefinitionBodyBase.java
+++ b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/typedef/GrTypeDefinitionBodyBase.java
@@ -1,4 +1,4 @@
-// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package org.jetbrains.plugins.groovy.lang.psi.impl.statements.typedef;
 
 import com.intellij.lang.ASTNode;
@@ -193,7 +193,7 @@ public abstract class GrTypeDefinitionBodyBase extends GrStubElementBase<EmptySt
   }
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean before) {
     ASTNode afterLast = last.getTreeNext();
     ASTNode next;
     for (ASTNode child = first; child != afterLast; child = next) {
diff --git a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/typedef/members/GrMethodImpl.java b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/typedef/members/GrMethodImpl.java
index 9647959c15b9..d105c0a2cd3a 100644
--- a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/typedef/members/GrMethodImpl.java
+++ b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/statements/typedef/members/GrMethodImpl.java
@@ -1,4 +1,4 @@
-// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package org.jetbrains.plugins.groovy.lang.psi.impl.statements.typedef.members;
 
 import com.intellij.lang.ASTNode;
@@ -23,7 +23,7 @@ public class GrMethodImpl extends GrMethodBaseImpl implements GrMethod {
   }
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean before) {
     if (first == last && first.getPsi() instanceof GrTypeParameterList) {
       if (!getModifierList().hasExplicitVisibilityModifiers()) {
         getModifierList().setModifierProperty(GrModifier.DEF, true);
diff --git a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/types/GrTypeArgumentListImpl.java b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/types/GrTypeArgumentListImpl.java
index ffb3b46ac626..2b5277c250be 100644
--- a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/types/GrTypeArgumentListImpl.java
+++ b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/types/GrTypeArgumentListImpl.java
@@ -1,4 +1,4 @@
-// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package org.jetbrains.plugins.groovy.lang.psi.impl.types;
 
 import com.intellij.lang.ASTNode;
@@ -64,7 +64,7 @@ public class GrTypeArgumentListImpl extends GroovyPsiElementImpl implements GrTy
   }
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean before) {
     if (first == last && first.getPsi() instanceof GrTypeElement) {
       if (anchor == null) {
         anchor = getLastChild().getNode();
diff --git a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/types/GrTypeParameterListImpl.java b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/types/GrTypeParameterListImpl.java
index 4ca40d35b9da..8fd9628cc18b 100644
--- a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/types/GrTypeParameterListImpl.java
+++ b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/types/GrTypeParameterListImpl.java
@@ -1,4 +1,4 @@
-// Copyright 2000-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package org.jetbrains.plugins.groovy.lang.psi.impl.types;
 
 import com.intellij.lang.ASTNode;
@@ -68,7 +68,7 @@ public class GrTypeParameterListImpl extends GrStubElementBase<EmptyStub>
   }
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean before) {
     appendParenthesesIfNeeded();
 
     if (first == last && first.getPsi() instanceof PsiTypeParameter) {
diff --git a/python/python-psi-impl/src/com/jetbrains/python/psi/impl/PyFromImportStatementImpl.java b/python/python-psi-impl/src/com/jetbrains/python/psi/impl/PyFromImportStatementImpl.java
index 43deefbd1fee..2e238dc456a0 100644
--- a/python/python-psi-impl/src/com/jetbrains/python/psi/impl/PyFromImportStatementImpl.java
+++ b/python/python-psi-impl/src/com/jetbrains/python/psi/impl/PyFromImportStatementImpl.java
@@ -139,7 +139,7 @@ public class PyFromImportStatementImpl extends PyBaseElementImpl<PyFromImportSta
   }
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean before) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean before) {
     boolean addingNewName = first == last &&
                             first.getElementType() == PyElementTypes.IMPORT_ELEMENT &&
                             (anchor == null || anchor.getElementType() == PyElementTypes.IMPORT_ELEMENT);
diff --git a/xml/xml-psi-impl/src/com/intellij/psi/impl/source/xml/XmlStubBasedTagBase.java b/xml/xml-psi-impl/src/com/intellij/psi/impl/source/xml/XmlStubBasedTagBase.java
index 6cff419c019f..9357000421c4 100644
--- a/xml/xml-psi-impl/src/com/intellij/psi/impl/source/xml/XmlStubBasedTagBase.java
+++ b/xml/xml-psi-impl/src/com/intellij/psi/impl/source/xml/XmlStubBasedTagBase.java
@@ -1,4 +1,4 @@
-// Copyright 2000-2022 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+// Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.psi.impl.source.xml;
 
 import com.intellij.lang.ASTNode;
@@ -293,7 +293,7 @@ public class XmlStubBasedTagBase<StubT extends XmlTagStub<?>>
   }
 
   @Override
-  public ASTNode addInternal(ASTNode first, ASTNode last, ASTNode anchor, Boolean beforeB) {
+  public ASTNode addInternal(@NotNull ASTNode first, @NotNull ASTNode last, ASTNode anchor, Boolean beforeB) {
     if (!(first instanceof TreeElement)) return null;
     TreeElement firstAppended = null;
     boolean before = beforeB == null || beforeB.booleanValue();