Fatal error: Uncaught Error: Attempt to assign property "versions" on null in /scalar-data/scalar.usc.edu/works/system/application/libraries/RDF_Object.php:407 Stack trace: #0 /scalar-data/scalar.usc.edu/works/system/application/libraries/RDF_Object.php(1038): RDF_Object->_content(NULL, Array) #1 /scalar-data/scalar.usc.edu/works/system/application/libraries/RDF_Object.php(911): RDF_Object->_annotation_child(Object(stdClass), Array) #2 /scalar-data/scalar.usc.edu/works/system/application/libraries/RDF_Object.php(445): RDF_Object->_relationships(Object(stdClass), Array) #3 /scalar-data/scalar.usc.edu/works/system/application/libraries/RDF_Object.php(981): RDF_Object->_content(Object(stdClass), Array) #4 /scalar-data/scalar.usc.edu/works/system/application/libraries/RDF_Object.php(902): RDF_Object->_annotation_parent(Object(stdClass), Array) #5 /scalar-data/scalar.usc.edu/works/system/application/libraries/RDF_Object.php(445): RDF_Object->_relationships(Object(stdClass), Array) #6 /scalar-data/scalar.usc.edu/works/system/application/libraries/RDF_Object.php(338): RDF_Object->_content(Object(stdClass), Array) #7 /scalar-data/scalar.usc.edu/works/system/application/libraries/RDF_Object.php(200): RDF_Object->_index(Array) #8 /scalar-data/scalar.usc.edu/works/system/application/controllers/book.php(138): RDF_Object->index(Array) #9 /scalar-data/scalar.usc.edu/works/system/core/CodeIgniter.php(326): Book->_remap('real-food-chall...', Array) #10 /scalar-data/scalar.usc.edu/works/codeigniter.php(203): require_once('/scalar-data/sc...') #11 {main} thrown in /scalar-data/scalar.usc.edu/works/system/application/libraries/RDF_Object.php on line 407