diff --git a/core/src/main/java/org/apache/calcite/sql/type/ReturnTypes.java b/core/src/main/java/org/apache/calcite/sql/type/ReturnTypes.java
index 48da8b8..5924f00 100644
--- a/core/src/main/java/org/apache/calcite/sql/type/ReturnTypes.java
+++ b/core/src/main/java/org/apache/calcite/sql/type/ReturnTypes.java
@@ -574,13 +574,13 @@
                 RelDataType type =
                     opBinding.getOperandType(index)
                         .getComponentType();
-                assert type != null;
+                if (type == null) {
+                  return opBinding.getTypeFactory().createSqlType(SqlTypeName.NULL);
+                }
                 return type;
               }
 
-              @Override public int size() {
-                return opBinding.getOperandCount();
-              }
+              @Override public int size() { return opBinding.getOperandCount(); }
             });
     RelDataType biggestElementType =
         LEAST_RESTRICTIVE.inferReturnType(newBinding);
diff --git a/core/src/test/java/org/apache/calcite/test/SqlValidatorTest.java b/core/src/test/java/org/apache/calcite/test/SqlValidatorTest.java
index df221d0..fff0fc2 100644
--- a/core/src/test/java/org/apache/calcite/test/SqlValidatorTest.java
+++ b/core/src/test/java/org/apache/calcite/test/SqlValidatorTest.java
@@ -1934,6 +1934,10 @@
         .columnType("DOUBLE NOT NULL");
     expr("element(multiset[multiset[cast(null as tinyint)]])")
         .columnType("TINYINT MULTISET NOT NULL");
+    // Test case for <a href="https://issues.apache.org/jira/projects/CALCITE/issues/CALCITE-6227">
+    // ELEMENT(NULL) causes an assertion failure</a>.
+    expr("element(null)")
+        .columnType("NULL");
   }
 
   @Test void testMemberOf() {