diff --git a/reactor/Core/src/jetbrains/mps/logic/reactor/util/ClassicTermTrie.kt b/reactor/Core/src/jetbrains/mps/logic/reactor/util/ClassicTermTrie.kt
index 835421b5..4dab8c4a 100644
--- a/reactor/Core/src/jetbrains/mps/logic/reactor/util/ClassicTermTrie.kt
+++ b/reactor/Core/src/jetbrains/mps/logic/reactor/util/ClassicTermTrie.kt
@@ -147,7 +147,7 @@ class ClassicTermTrie<T> : TermTrie<T> {
             WILDCARD
 
         } else {
-            term.symbol()
+            term.symbol() ?: throw NullPointerException("term symbol can't be null")
         }
     }