Adds extensios for ProcessBuilder for Null or Empty string checks.

[phillipsj]

I find myself writing this code a lot:

var builder = new ProcessArgumentBuilder();

if(!string.IsNullOrWhitespace(settings.MySetting){
    builder.Append(settings.MySetting);
}

I would like to add the following extension method or method to the ProcessArgumentBuilder to make this scenario easier.

public static ProcessArgumentBuilder AppendIfNotNullOrWhitespace(this ProcessArgumentBuilder builder, string setting){
    return !string.IsNullOrWhitespace(setting)? builder.Append(setting) : builder;
}

Then the code would look like this:

var builder = new ProcessArgumentBuilder();
builder.AppendIfNotNullOrWhitespace(settings.MySetting);

I think the name could be made shorter.

[mvput]

Is this up for grabs?

[devlead]

Don't think @cake-build/cake-team has looked at this one yet.

This possibly misses the scenario where it often is a key value pair and you in many cases want to omit the key too.
Perhaps something builder.IfNotNullOrWhitespace(settings?.MySetting?.ToString(), (pb, text)=>pb.AppendSwitchSecret("MySetting", text)
via something like public static ProcessArgumentBuilder IfNotNullOrWhitespace(this ProcessArgumentBuilder builder, string value, Func<ProcessArgumentBuilder, T, ProcessArgumentBuilder> func)
could handle that scenario.

[patriksvensson]

I agree with @devlead here. It will be too many variations of this otherwise.