Remove closing tag in form tag's extra hidden fields

The fields returned from a RequestDataValueProcessor are now
written as hidden fields without a closing tag.

Before:
<input type="hidden" name="xxx" value="yyy"></input>

After:
<input type="hidden" name="xxx" value="yyy" />

Issue: SPR-10103

Author: rstoyanchev

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/FormTag.java

@@ -469,8 +469,8 @@ private void writeHiddenFields(Map<String, String> hiddenFields) throws JspExcep
 		if (hiddenFields != null) {
 			for (String name : hiddenFields.keySet()) {
 				this.tagWriter.appendValue("<input type=\"hidden\" ");
-				this.tagWriter.appendValue("name=\"" + name + "\" value=\"" + hiddenFields.get(name) + "\">");
-				this.tagWriter.appendValue("</input>\n");
+				this.tagWriter.appendValue("name=\"" + name + "\" value=\"" + hiddenFields.get(name) + "\" ");
+				this.tagWriter.appendValue("/>\n");
 			}
 		}
 	}

spring-webmvc/src/test/java/org/springframework/web/servlet/tags/form/FormTagTests.java

@@ -293,7 +293,7 @@ public void testRequestDataValueProcessorHooks() throws Exception {
 
 		String output = getOutput();
 
-		assertEquals("<input type=\"hidden\" name=\"key\" value=\"value\"></input>", getInputTag(output));
+		assertEquals("<input type=\"hidden\" name=\"key\" value=\"value\" />", getInputTag(output));
 		assertFormTagOpened(output);
 		assertFormTagClosed(output);