public SendGridBuilder apiKey(String... key) {
		for (String k : key) {
			if (k != null) {
				apiKeys.add(k);
			}
		}
		return this;
	}
public SendGridBuilder apiKey ( String ... key ) { for ( String k : key ) { if ( k != null ) { apiKeys . add ( k ) ; } } return this ; }
Set SendGrid <a href=
"https://sendgrid.com/docs/Classroom/Send/How_Emails_Are_Sent/api_keys.html">API
key</a>.

You can specify a direct value. For example:

<pre>
.apiKey("localhost");
</pre>

<p>
You can also specify one or several property keys. For example:

<pre>
.apiKey("${custom.property.high-priority}", "${custom.property.low-priority}");
</pre>

The properties are not immediately evaluated. The evaluation will be done
when the {@link #build()} method is called.

If you provide several property keys, evaluation will be done on the
first key and if the property exists (see {@link EnvironmentBuilder}),
its value is used. If the first property doesn't exist in properties,
then it tries with the second one and so on.

@param key
one value, or one or several property keys
@return this instance for fluent chaining