diff --git a/jps/jps-plugin/src/org/jetbrains/kotlin/jps/targets/KotlinJvmModuleBuildTarget.kt b/jps/jps-plugin/src/org/jetbrains/kotlin/jps/targets/KotlinJvmModuleBuildTarget.kt
index 25fb049..35b3de9 100644
--- a/jps/jps-plugin/src/org/jetbrains/kotlin/jps/targets/KotlinJvmModuleBuildTarget.kt
+++ b/jps/jps-plugin/src/org/jetbrains/kotlin/jps/targets/KotlinJvmModuleBuildTarget.kt
@@ -381,6 +381,9 @@
             val className = generatedClass.outputClass.className
             if (!cache.isMultifileFacade(className)) return emptySet()
 
+            // In case of graph implementation of JPS
+            if (previousMappings == null) return emptySet()
+
             val name = previousMappings.getName(className.internalName)
             return previousMappings.getClassSources(name).toSet()
         }