1 files changed, 7 insertions, 1 deletions

diff --git a/subprojects/store-query/src/main/java/tools/refinery/store/query/substitution/Substitutions.java b/subprojects/store-query/src/main/java/tools/refinery/store/query/substitution/Substitutions.java
index 26cf1a20..5d4654da 100644
--- a/subprojects/store-query/src/main/java/tools/refinery/store/query/substitution/Substitutions.java
+++ b/subprojects/store-query/src/main/java/tools/refinery/store/query/substitution/Substitutions.java
@@ -1,6 +1,8 @@
 package tools.refinery.store.query.substitution;
 
-import tools.refinery.store.query.Variable;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import tools.refinery.store.query.term.Variable;
 
 import java.util.Map;
 
@@ -24,4 +26,8 @@ public final class Substitutions {
         public static Substitution renewing() {
                 return new RenewingSubstitution();
         }
+
+        public static Substitution compose(@Nullable Substitution first, @NotNull Substitution second) {
+                return first == null ? second : first.andThen(second);
+        }
 }