Apply suggestions from code review

Author: david-waltermire

core/src/main/java/gov/nist/secauto/metaschema/core/metapath/DynamicContext.java

@@ -326,7 +326,9 @@ public void pushExecutionStack(@NonNull IExpression expression) {
    */
   public void popExecutionStack(@NonNull IExpression expression) {
     IExpression popped = this.sharedState.executionStack.pop();
-    assert expression.equals(popped);
+    if (!expression.equals(popped)) {
+        throw new IllegalStateException("Popped expression does not match expected expression");
+    }
   }
 
   /**