Avoid NPE in debugPrint() when owner is null

PiperOrigin-RevId: 414390111
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcLinkingContext.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcLinkingContext.java
index c736a72..02ad695 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcLinkingContext.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcLinkingContext.java
@@ -276,7 +276,11 @@
     @Override
     public void debugPrint(Printer printer) {
       printer.append("<LinkerInput(owner=");
-      owner.debugPrint(printer);
+      if (owner == null) {
+        printer.append("[null owner, uses old create_linking_context API]");
+      } else {
+        owner.debugPrint(printer);
+      }
       printer.append(", libraries=[");
       for (LibraryToLink libraryToLink : libraries) {
         libraryToLink.debugPrint(printer);