diff --git a/python/python-ast/src/com/jetbrains/python/ast/PyAstBinaryExpression.java b/python/python-ast/src/com/jetbrains/python/ast/PyAstBinaryExpression.java
index 351b42582a75..211083b45208 100644
--- a/python/python-ast/src/com/jetbrains/python/ast/PyAstBinaryExpression.java
+++ b/python/python-ast/src/com/jetbrains/python/ast/PyAstBinaryExpression.java
@@ -8,6 +8,7 @@ import com.intellij.psi.tree.IElementType;
 import com.intellij.psi.util.PsiTreeUtil;
 import com.intellij.psi.util.QualifiedName;
 import com.intellij.util.ObjectUtils;
+import com.intellij.util.containers.ContainerUtil;
 import com.jetbrains.python.PyNames;
 import com.jetbrains.python.PyTokenTypes;
 import com.jetbrains.python.ast.impl.PyPsiUtilsCore;
@@ -17,7 +18,6 @@ import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import java.util.Collections;
 import java.util.List;
 
 
@@ -109,8 +109,9 @@ public interface PyAstBinaryExpression extends PyAstQualifiedExpression, PyAstCa
   }
 
   @Override
-  default @NotNull List<? extends PyAstExpression> getArguments(@Nullable PyAstCallable resolvedCallee) {
-    return Collections.singletonList(isRightOperator(resolvedCallee) ? getChainedComparisonAwareLeftExpression() : getRightExpression());
+  default @NotNull List<@NotNull PyAstExpression> getArguments(@Nullable PyAstCallable resolvedCallee) {
+    PyAstExpression operand = isRightOperator(resolvedCallee) ? getChainedComparisonAwareLeftExpression() : getRightExpression();
+    return ContainerUtil.createMaybeSingletonList(operand);
   }
 
   private @Nullable PyAstExpression getChainedComparisonAwareLeftExpression() {
diff --git a/python/python-ast/src/com/jetbrains/python/ast/PyAstCallExpression.java b/python/python-ast/src/com/jetbrains/python/ast/PyAstCallExpression.java
index 1d6284ef2299..48aa26bf6de7 100644
--- a/python/python-ast/src/com/jetbrains/python/ast/PyAstCallExpression.java
+++ b/python/python-ast/src/com/jetbrains/python/ast/PyAstCallExpression.java
@@ -50,7 +50,7 @@ public interface PyAstCallExpression extends PyAstCallSiteExpression {
   }
 
   @Override
-  default @NotNull List<PyAstExpression> getArguments(@Nullable PyAstCallable resolvedCallee) {
+  default @NotNull List<@NotNull PyAstExpression> getArguments(@Nullable PyAstCallable resolvedCallee) {
     return Arrays.asList(getArguments());
   }
 
diff --git a/python/python-ast/src/com/jetbrains/python/ast/PyAstCallSiteExpression.java b/python/python-ast/src/com/jetbrains/python/ast/PyAstCallSiteExpression.java
index bccf9b27c549..0449d4aa7d34 100644
--- a/python/python-ast/src/com/jetbrains/python/ast/PyAstCallSiteExpression.java
+++ b/python/python-ast/src/com/jetbrains/python/ast/PyAstCallSiteExpression.java
@@ -42,5 +42,5 @@ public interface PyAstCallSiteExpression extends PyAstExpression {
   PyAstExpression getReceiver(@Nullable PyAstCallable resolvedCallee);
 
   @NotNull
-  List<? extends PyAstExpression> getArguments(@Nullable PyAstCallable resolvedCallee);
+  List<? extends @NotNull PyAstExpression> getArguments(@Nullable PyAstCallable resolvedCallee);
 }
diff --git a/python/python-ast/src/com/jetbrains/python/ast/PyAstPrefixExpression.java b/python/python-ast/src/com/jetbrains/python/ast/PyAstPrefixExpression.java
index d90ad3d89e1d..fad94d769762 100644
--- a/python/python-ast/src/com/jetbrains/python/ast/PyAstPrefixExpression.java
+++ b/python/python-ast/src/com/jetbrains/python/ast/PyAstPrefixExpression.java
@@ -25,7 +25,7 @@ public interface PyAstPrefixExpression extends PyAstQualifiedExpression, PyAstRe
   }
 
   @Override
-  default @NotNull List<PyAstExpression> getArguments(@Nullable PyAstCallable resolvedCallee) {
+  default @NotNull List<@NotNull PyAstExpression> getArguments(@Nullable PyAstCallable resolvedCallee) {
     return Collections.emptyList();
   }
 
diff --git a/python/python-ast/src/com/jetbrains/python/ast/PyAstSubscriptionExpression.java b/python/python-ast/src/com/jetbrains/python/ast/PyAstSubscriptionExpression.java
index 6e9a61c7c313..44f5c3a8c9d3 100644
--- a/python/python-ast/src/com/jetbrains/python/ast/PyAstSubscriptionExpression.java
+++ b/python/python-ast/src/com/jetbrains/python/ast/PyAstSubscriptionExpression.java
@@ -2,8 +2,8 @@
 package com.jetbrains.python.ast;
 
 import com.intellij.lang.ASTNode;
-import com.intellij.psi.PsiElement;
 import com.intellij.psi.util.QualifiedName;
+import com.intellij.util.containers.ContainerUtil;
 import com.jetbrains.python.PyNames;
 import com.jetbrains.python.PyTokenTypes;
 import com.jetbrains.python.PythonDialectsTokenSetProvider;
@@ -13,7 +13,7 @@ import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import java.util.Arrays;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
@@ -27,14 +27,13 @@ public interface PyAstSubscriptionExpression extends PyAstQualifiedExpression, P
   }
 
   @Override
-  default @NotNull List<PyAstExpression> getArguments(@Nullable PyAstCallable resolvedCallee) {
-    if (AccessDirection.of(this) == AccessDirection.WRITE) {
-      final PsiElement parent = getParent();
-      if (parent instanceof PyAstAssignmentStatement) {
-        return Arrays.asList(getIndexExpression(), ((PyAstAssignmentStatement)parent).getAssignedValue());
-      }
+  default @NotNull List<@NotNull PyAstExpression> getArguments(@Nullable PyAstCallable resolvedCallee) {
+    List<PyAstExpression> result = new ArrayList<>();
+    ContainerUtil.addIfNotNull(result, getIndexExpression());
+    if (AccessDirection.of(this) == AccessDirection.WRITE && getParent() instanceof PyAstAssignmentStatement assignment) {
+      ContainerUtil.addIfNotNull(result, assignment.getAssignedValue());
     }
-    return Collections.singletonList(getIndexExpression());
+    return Collections.unmodifiableList(result);
   }
 
   /**
diff --git a/python/python-psi-api/src/com/jetbrains/python/psi/PyCallSiteExpression.java b/python/python-psi-api/src/com/jetbrains/python/psi/PyCallSiteExpression.java
index 48374fa13ed4..e1592a7208ba 100644
--- a/python/python-psi-api/src/com/jetbrains/python/psi/PyCallSiteExpression.java
+++ b/python/python-psi-api/src/com/jetbrains/python/psi/PyCallSiteExpression.java
@@ -28,8 +28,8 @@ public interface PyCallSiteExpression extends PyAstCallSiteExpression, PyExpress
     return (PyExpression)getReceiver((PyAstCallable)resolvedCallee);
   }
 
-  default @NotNull List<PyExpression> getArguments(@Nullable PyCallable resolvedCallee) {
+  default @NotNull List<@NotNull PyExpression> getArguments(@Nullable PyCallable resolvedCallee) {
     //noinspection unchecked
-    return (List<PyExpression>)getArguments((PyAstCallable)resolvedCallee);
+    return (List<@NotNull PyExpression>)getArguments((PyAstCallable)resolvedCallee);
   }
 }
diff --git a/python/python-psi-impl/src/com/jetbrains/python/psi/impl/PyCallExpressionHelper.kt b/python/python-psi-impl/src/com/jetbrains/python/psi/impl/PyCallExpressionHelper.kt
index 3a2d808155cf..60d965483b0d 100644
--- a/python/python-psi-impl/src/com/jetbrains/python/psi/impl/PyCallExpressionHelper.kt
+++ b/python/python-psi-impl/src/com/jetbrains/python/psi/impl/PyCallExpressionHelper.kt
@@ -1025,14 +1025,10 @@ fun analyzeArguments(
       }
       else if (!allPositionalArguments.isEmpty()) {
         val positionalArgument = allPositionalArguments.next()
-        if (positionalArgument != null) {
-          mappedParameters.put(positionalArgument, parameter)
-          if (positionalComponentsOfVariadicArguments.contains(positionalArgument)) {
-            parametersMappedToVariadicPositionalArguments.add(parameter)
-          }
-        }
-        else if (!parameter.hasDefaultValue()) {
-          unmappedParameters.add(parameter)
+        assert(positionalArgument != null)
+        mappedParameters.put(positionalArgument, parameter)
+        if (positionalComponentsOfVariadicArguments.contains(positionalArgument)) {
+          parametersMappedToVariadicPositionalArguments.add(parameter)
         }
       }
       else {