Clarify setHeader() and null or empty string arguments

[glassfishrobot]

The spec for HttpServletResponse.setHeader() does not say what to do if one or both of the arguments is null or empty.

https://docs.oracle.com/javaee/7/api/javax/servlet/http/HttpServletResponse.html#setHeader-java.lang.String-java.lang.String-

[glassfishrobot]

@glassfishrobot Commented
Reported by @edburns

[glassfishrobot]

@glassfishrobot Commented
@edburns said:
setHeader(null, anything) is a no-op.
setHeader(anything, null) removes the header
setHeader(anything, "") makes the header "anything" have an empty value. If there is an existing value for header anything, that value is replaced with the empty value.

If a header has been removed in this way, containsHeader() for that header returns false.

containsHeader(null) always returns false.

[glassfishrobot]

@glassfishrobot Commented
@edburns said:
Add this text:

"Containers may still add or modify headers before the response is
committed. These will generally be headers that are required at a
protocol level."

[glassfishrobot]

@glassfishrobot Commented
This issue was imported from java.net JIRA SERVLET_SPEC-159

[glassfishrobot]

• Issue Imported From: https://github.com/javaee/servlet-spec/issues/159
• Original Issue Raised By:@glassfishrobot
• Original Issue Assigned To: @glassfishrobot