Description:
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The documentation of cURL regarding the CURLOPT_CUSTOMREQUEST option mentions the following:

> Restore to the internal default by setting this to NULL.

Source: http://curl.haxx.se/libcurl/c/curl_easy_setopt.html#CURLOPTCUSTOMREQUEST

However, the option value gets cast to a string before the call to curl_easy_setopt() is made, thus changing the NULL value to an empty string. It should be possible to reset the internal behaviour by passing a NULL value, i.e.

> curl_setopt($ch, CURLOPT_CUSTOMREQUEST, NULL);

This problem is also highlighted in this SO question: http://stackoverflow.com/questions/4163865/how-to-reset-curlopt-customrequest

Test script:
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$ch = curl_init('http://localhost');

curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'DELETE');
curl_exec($ch);

curl_setopt($ch, CURLOPT_CUSTOMREQUEST, NULL);
curl_exec($ch);


Expected result:
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One DELETE request followed by one GET request.

Actual result:
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One DELETE request followed by an invalid request (i.e. ` / HTTP/1.1`)