clean code

lib/src/bones_api_condition_sql.dart

@@ -498,11 +498,21 @@ class ConditionSQLEncoder extends ConditionEncoder {
       );
     }
 
-    final keys = c.keys.cast<ConditionKeyField>();
+    final keys = c.keys;
     if (keys.isEmpty) {
       throw ConditionEncodingError('Empty key path: $c');
     }
 
+    ConditionKeyField getKey(int index) {
+      var k = keys[index];
+      if (k is! ConditionKeyField) {
+        throw ConditionEncodingError(
+          "key[$index] is not a `ConditionKeyField`: $k",
+        );
+      }
+      return k;
+    }
+
     FutureOr<MapEntry<Type, String>> walkKeys({
       required int index,
       required String sourceTable,
@@ -512,7 +522,7 @@ class ConditionSQLEncoder extends ConditionEncoder {
           schemeProvider: schemeProvider,
           context: context,
           targetTable: sourceTable,
-          key: keys[index],
+          key: getKey(index),
         );
       }
 
@@ -527,7 +537,7 @@ class ConditionSQLEncoder extends ConditionEncoder {
           c: c,
           sourceScheme: scheme,
           sourceTable: sourceTable,
-          key: keys[index],
+          key: getKey(index),
         ).resolveMapped(
           (nextTable) => walkKeys(index: index + 1, sourceTable: nextTable),
         );

lib/src/bones_api_entity_db_sql.dart

@@ -60,8 +60,12 @@ extension on List<_JoinEntry> {
   /// ordered correctly, or `false` if a best-effort fallback order was used.
   bool sortJoins(Set<String> initialAliases) {
     final List<_JoinEntry> joins = this;
-    // No ordering needed for zero or one JOIN.
-    if (joins.length <= 1) {
+    // No ordering needed for zero JOINs:
+    if (joins.isEmpty) {
+      return true;
+    }
+    // No ordering needed for a single JOIN; only check if it is resolved:
+    else if (joins.length == 1) {
       var resolved = joins.first.refsResolved(initialAliases);
       return resolved;
     }