Index: wp-includes/option.php
===================================================================
--- wp-includes/option.php	(revision 31079)
+++ wp-includes/option.php	(working copy)
@@ -81,6 +81,10 @@
 					$value = $row->option_value;
 					wp_cache_add( $option, $value, 'options' );
 				} else { // option does not exist, so we must cache its non-existence
+					// check to make sure $notoptions is an array
+					if ( !is_array( $notoptions ) ) {
+						$notoptions = array();
+					}
 					$notoptions[$option] = true;
 					wp_cache_set( 'notoptions', $notoptions, 'options' );
 
@@ -985,6 +989,10 @@
 				$value = maybe_unserialize( $value );
 				wp_cache_set( $cache_key, $value, 'site-options' );
 			} else {
+				// check to make sure $notoptions is an array
+				if ( !is_array( $notoptions ) ) {
+					$notoptions = array();
+				}
 				$notoptions[$option] = true;
 				wp_cache_set( $notoptions_key, $notoptions, 'site-options' );