diff --git a/platform/platform-api/src/com/intellij/execution/configurations/ParamsGroup.java b/platform/platform-api/src/com/intellij/execution/configurations/ParamsGroup.java
index 6a5ed4631b4f..2cbf04868a40 100644
--- a/platform/platform-api/src/com/intellij/execution/configurations/ParamsGroup.java
+++ b/platform/platform-api/src/com/intellij/execution/configurations/ParamsGroup.java
@@ -53,7 +53,7 @@ public class ParamsGroup implements Cloneable {
     myGroupParams.addAt(index, parameter);
   }
 
-  public void addParameters(final String... parameters) {
+  public void addParameters(@NotNull final String... parameters) {
     for (String parameter : parameters) {
       addParameter(parameter);
     }
diff --git a/python/src/com/jetbrains/python/testing/tox/PyToxConfiguration.java b/python/src/com/jetbrains/python/testing/tox/PyToxConfiguration.java
index 8ec2bc801223..0082c5b00e8b 100644
--- a/python/src/com/jetbrains/python/testing/tox/PyToxConfiguration.java
+++ b/python/src/com/jetbrains/python/testing/tox/PyToxConfiguration.java
@@ -128,7 +128,9 @@ public final class PyToxConfiguration extends AbstractPythonRunConfiguration<PyT
 
   @Override
   public void addTestSpecsAsParameters(@NotNull final ParamsGroup paramsGroup, @NotNull final List<String> testSpecs) {
-    paramsGroup.addParameters(myArguments);
+    if (myArguments != null) {
+      paramsGroup.addParameters(myArguments);
+    }
     if (!testSpecs.isEmpty()) {
       paramsGroup.addParameter(String.format("-e %s", StringUtil.join(testSpecs, ",")));
     }