PHP Warning: Attempt to read property “id” on null

$product->id only works if $product has a value, and sometimes it does not! E.g. on a login page which product would it be?

So you need to check if it’s valid/exists/safe with an if check:

global $product;
if ( ! empty( $product ) ) {
    // code that uses $product goes here
}

Related Posts:

  1. How to add elements to an empty array in PHP?
  2. Where to get information about array fields in $_REQUEST?
  3. Pass a PHP variable to another file
  4. How to store the_title() into a variable to reutrn the value, not just echo it
  5. Variables declared in header not available in other includes
  6. How do I make my function add variables/values to the $post object?
  7. Cleanest/Fastest way to avoid calling and retrieving data from the database multiple times?
  8. where to include a php file
  9. How do I know what variables are passed in a filter/action and what their meaning is?
  10. When would you use $_post instead of $post?
  11. Locating Global Variables
  12. Pass PHP variable to JavaScript without inline JS
  13. Count the number of times the search form template gets included on a page
  14. Putting PHP variables into javascript [duplicate]
  15. Variable global scope [closed]
  16. How to rewrite URL with PHP variables with htaccess to a normal looking URL?
  17. Using a variable in is_page(array())
  18. Static variable and add_rewrite_rule?
  19. How to put a variable in a instance in the widget
  20. Call global variable array() in woocommerce child/template
  21. get_term_link() returns correct – But illogical error-messages disturb
  22. How can I Add a variable PHP in the Menu Nav
  23. Pass variable from one function to another
  24. Get value from shortcode to do something
  25. PHP, Creating a dynamic variable
  26. How to modify a global variable in a function and use it on another function?
  27. Variable not staying set
  28. WordPress function and string as variable?
  29. Create a WordPress shortcode using PHP [duplicate]
  30. How to pass a PHP $_GET variable and fetch/output it?
  31. Creating WordPress Shortcode with Variable
  32. How to put a form with php code into a variable or shortcode?
  33. Apply class to every third list item? [duplicate]
  34. persist a variable set in header.php all the way down to footer.php
  35. Get access to variable from previous pageview, excluding ajax-calls
  36. How to deal with too many $_POST variable conditions from ajax request at backend? [closed]
  37. What is the alternative code to if (isset ($_POST) && !empty ($_POST) to avoid warnings?
  38. How to pass a variable to get_template_part that’s updated every time the template part is called?
  39. Insert page content into another page with a changed variable
  40. Pass Variables or Variable Place-Holder from Editor to PHP
  41. How to access or parse key/values that have “string”
  42. How Do I Find & Remove H1 From Site-Title-Wrapper? [closed]
  43. Changing the order of custom fields in the dashboard for Woocommerce variable products [closed]
  44. javascript variable to wordpress php variable
  45. How to reference PHP in Javascript
  46. Store and Change Session variable – PHP SESSION VARIABLE
  47. Overide Variable in Child Theme
  48. echo var into wp_query
  49. how can I include some custom variable from functions.php?
  50. Dynamically adding filters
  51. PHP variables in a post?
  52. WordPress is removing query variables like page, p from the URL of a custom static page
  53. How to send a php var to jQuery Ajax call with two different file
  54. Unable to display multiple parameters from url by javascript through shortcodes
  55. How to check a variable Changes
  56. global $product is empty string when passed into function
  57. Can’t pass var from php wp_ajax into ajax script : result undefined or null
  58. Custom global variable not working in function
  59. WordPress How do I pass a variable from one add_action to another?
  60. Best way to use variables in multiple functions?
  61. Trying to add some custom text into WordPress Post title via function.php
  62. Reduce Stock Based on Custom Variation Field Rather than Attribute (Working Script)
  63. How do I fix Undefined variable using $_POST in function?
  64. How to change the value of a variable using input field?
  65. How to find php variable of wordpress theme settings
  66. Add class to all meta boxes for a custom post type
  67. Passing parameter from the current URL to redirect to another url
  68. Undefined variable & issue with smof_data
  69. Pulling a variable into the wp_nav_menu function
  70. Where can I find the declaration of `$_wp_theme_features`?
  71. Child theme functions.php file change database entries
  72. Custom Taxonomy Link Text Echo Name Not Slug
  73. how to add number value in front for variable [closed]
  74. Create and update Custom Cookie based on multiple GET and POST Values for first time visitors?
  75. Difference in Get Variable Location
  76. If I define a variable in header.php, how do I make it available to templates?
  77. Shortcode not passing variable to included file
  78. ACF allow zero as a value
  79. Can’t get options with $data[‘variable’]
  80. PHP Use Declared array Variable inside already Declared Array
  81. Import and use a variable in additional settings of Contact Form 7 [closed]
  82. Use ajax response in PHP function
  83. WP query with variables gives no result for specific user
  84. How can one use variables in a template or template part without polluting the global scope?
  85. How to make my scroll bar show under condition
  86. What does the token %1$s in WordPress represent [closed]
  87. PHP/Manual use of images? – 2 Questions
  88. Remove class that has been added by parent theme
  89. Create Logout Link WordPress Admin Menu
  90. Display post image with fancybox
  91. WordPress 3.2 query_posts and pagination, permalinks issue
  92. Shortcode with PHP issue “Undefined index”
  93. Accidentally deleted php code in WordPress website [closed]
  94. WordPress Twenty Eleven PhP – forcing php code to skip first post on homepage?
  95. Problem with data collection in tables
  96. Redirecting the lost password page request when using a custon login page
  97. Form not working as it should in WordPress, but in a normal HTML site it does
  98. How do I create a single WordPress page that will use PHP to include different HTML files based on a vaule in the URL?
  99. Forbid certain users to access a specific page
  100. Remove content links (internal and external), but exclude post at specific categories