Guard against returning NULL or empty node names

rcl/include/rcl/graph.h

@@ -406,7 +406,6 @@ rcl_names_and_types_fini(rcl_names_and_types_t * names_and_types);
  *
  * The `node_names` parameter must be allocated and zero initialized.
  * `node_names` is the output for this function, and contains allocated memory.
- * Note that entries in the array might contain `NULL` values.
  * Use rcutils_get_zero_initialized_string_array() for initializing an empty
  * rcutils_string_array_t struct.
  * This `node_names` struct should therefore be passed to rcutils_string_array_fini()
@@ -445,6 +444,8 @@ rcl_names_and_types_fini(rcl_names_and_types_t * names_and_types);
  * \return #RCL_RET_OK if the query was successful, or
  * \return #RCL_RET_BAD_ALLOC if an error occurred while allocating memory, or
  * \return #RCL_RET_INVALID_ARGUMENT if any arguments are invalid, or
+ * \return #RCL_RET_NODE_INVALID_NAME if a node with an invalid name is detected, or
+ * \return #RCL_RET_NODE_INVALID_NAMESPACE if a node with an invalid namespace is detected, or
  * \return #RCL_RET_ERROR if an unspecified error occurs.
  */
 RCL_PUBLIC

rcl/src/rcl/graph.c

@@ -341,7 +341,30 @@ rcl_get_node_names(
     rcl_node_get_rmw_handle(node),
     node_names,
     node_namespaces);
-  return rcl_convert_rmw_ret_to_rcl_ret(rmw_ret);
+
+  if (RMW_RET_OK != rmw_ret) {
+    return rcl_convert_rmw_ret_to_rcl_ret(rmw_ret);
+  }
+
+  // Check that none of the node names are NULL or empty
+  for (size_t i = 0u; i < node_names->size; ++i) {
+    if (!node_names->data[i]) {
+      RCL_SET_ERROR_MSG("NULL node name returned by the RMW layer");
+      return RCL_RET_NODE_INVALID_NAME;
+    }
+    if (!strcmp(node_names->data[i], "")) {
+      RCL_SET_ERROR_MSG("empty node name returned by the RMW layer");
+      return RCL_RET_NODE_INVALID_NAME;
+    }
+  }
+  // Check that none of the node namespaces are NULL
+  for (size_t i = 0u; i < node_namespaces->size; ++i) {
+    if (!node_namespaces->data[i]) {
+      RCL_SET_ERROR_MSG("NULL node namespace returned by the RMW layer");
+      return RCL_RET_NODE_INVALID_NAMESPACE;
+    }
+  }
+  return RCL_RET_OK;
 }
 
 rcl_ret_t