Don't add null module info to list

EA-113650 - TCE: LazyModuleDependencies.getModulesWhoseInternalsAreVisible

idea/idea-analysis/src/org/jetbrains/kotlin/idea/caches/resolve/IdeaModuleInfos.kt

@@ -1,17 +1,6 @@
 /*
- * Copyright 2010-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2000-2017 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.idea.caches.resolve
@@ -167,7 +156,7 @@ data class ModuleTestSourceInfo internal constructor(override val module: Module
         list.addIfNotNull(module.productionSourceInfo())
 
         TestModuleProperties.getInstance(module).productionModule?.let {
-            list.add(it.productionSourceInfo())
+            list.addIfNotNull(it.productionSourceInfo())
         }
 
         CachedValueProvider.Result(list, ProjectRootModificationTracker.getInstance(module.project))