Make sure that requests without a body don't set contentType, and a z…

…ero-length body is sent rather than null. Possible fix for #6811 and #6674.

src/ajax.js

@@ -4,6 +4,7 @@ var jsc = jQuery.now(),
 	rscript = /<script\b[^<]*(?:(?!<\/script>)<[^<]*)*<\/script>/gi,
 	rselectTextarea = /^(?:select|textarea)/i,
 	rinput = /^(?:color|date|datetime|email|hidden|month|number|password|range|search|tel|text|time|url|week)$/i,
+	rnoContent = /^(?:GET|HEAD|DELETE)$/,
 	rbracket = /\[\]$/,
 	jsre = /\=\?(&|$)/,
 	rquery = /\?/,
@@ -204,7 +205,7 @@ jQuery.extend({
 
 	ajax: function( origSettings ) {
 		var s = jQuery.extend(true, {}, jQuery.ajaxSettings, origSettings),
-			jsonp, status, data, type = s.type.toUpperCase();
+			jsonp, status, data, type = s.type.toUpperCase(), noContent = rnoContent.test(type);
 
 		s.url = s.url.replace( rhash, "" );
 
@@ -355,8 +356,8 @@ jQuery.extend({
 
 		// Need an extra try/catch for cross domain requests in Firefox 3
 		try {
-			// Set the correct header, if data is being sent
-			if ( s.data || origSettings && origSettings.contentType ) {
+			// Set content-type if data specified and content-body is valid for this type
+			if ( (s.data != null && !noContent) || (origSettings && origSettings.contentType) ) {
 				xhr.setRequestHeader("Content-Type", s.contentType);
 			}
 
@@ -491,7 +492,7 @@ jQuery.extend({
 
 		// Send the data
 		try {
-			xhr.send( (type !== "GET" && s.data) || null );
+			xhr.send( noContent || s.data == null ? null : s.data );
 
 		} catch( sendError ) {
 			jQuery.ajax.handleError( s, xhr, null, sendError );