diff --git a/src/Collector/ImplementedInterfaceCollector.php b/src/Collector/ImplementedInterfaceCollector.php
index 21bfe0f0..727361c2 100644
--- a/src/Collector/ImplementedInterfaceCollector.php
+++ b/src/Collector/ImplementedInterfaceCollector.php
@@ -18,7 +18,7 @@ public function getNodeType(): string
 
     /**
      * @param Class_ $node
-     * @return string[]|null
+     * @return non-empty-array<string>|null
      */
     public function processNode(Node $node, Scope $scope): ?array
     {
@@ -33,6 +33,10 @@ public function processNode(Node $node, Scope $scope): ?array
             $implementedInterfaceNames[] = $implement->toString();
         }
 
+        if ($implementedInterfaceNames === []) {
+            return null;
+        }
+
         return $implementedInterfaceNames;
     }
 }
diff --git a/src/Collector/InterfaceOfAbstractClassCollector.php b/src/Collector/InterfaceOfAbstractClassCollector.php
index 7601fc82..17c1fa76 100644
--- a/src/Collector/InterfaceOfAbstractClassCollector.php
+++ b/src/Collector/InterfaceOfAbstractClassCollector.php
@@ -18,7 +18,7 @@ public function getNodeType(): string
 
     /**
      * @param Class_ $node
-     * @return string[]|null
+     * @return non-empty-array<string>|null
      */
     public function processNode(Node $node, Scope $scope): ?array
     {
@@ -32,6 +32,10 @@ public function processNode(Node $node, Scope $scope): ?array
             $interfaceNames[] = $implement->toString();
         }
 
+        if ($interfaceNames === []) {
+            return null;
+        }
+
         return $interfaceNames;
     }
 }