Fixed NullPointerException Bug

[pingpingy1]

RequestTemplate.header(name, values) method has two overloaded implementations.
In the case where values has type Iterable<String>, values is guarded against null.
This does not happen when values has type String..., which is fixed by this commit.

Concrete testcase:

import feign.RequestTemplate;

public class Test{
	public static void main(String args[]) throws Exception {
		RequestTemplate rt = new RequestTemplate();
		String[] values = null;
		String name = "";
		rt.header(name, values); // NPE
	}
}

Result:

Exception in thread "main" java.lang.NullPointerException
        at java.base/java.util.Objects.requireNonNull(Objects.java:233)
        at java.base/java.util.Arrays$ArrayList.<init>(Arrays.java:4238)
        at java.base/java.util.Arrays.asList(Arrays.java:4223)
        at feign.RequestTemplate.header(RequestTemplate.java:706)
        at Test.main(Test.java:8)

[velo]

Hi, appreciated the effort you put into fixing this problem.

Seems your change includes some git syntax instructions, please fix that.

Also, It looks like nothing what changed on JacksonCodecTest, would you please revert the formatting changes?

Last, but also a blocked, please create a new test case inside RequestTemplateTest.java that reproduced the issue you found.

Thanks for the assistance

[pingpingy1]

@velo Thank you for the kind instructions.
I apologize for not fully obliging by the guidelines; this is my first public PR, and I was quite nervous.
Will promptly get on with it.

[velo]

this is my first public PR, and I was quite nervous

All good, you probably did far better than I did on my first one

[velo]

I will be releasing feign next Friday, this will be included

[pingpingy1]

Thank you for the encouraging messages sir!!

[velo]

Hey, I'm not going to get more help by being nasty

Look forward your next PR