code: public CloudhopperBuilder systemId(String... systemId) {
  		for (String s : systemId) {
  			if (s != null) {
  				systemIds.add(s);
  			}
  		}
  		return this;
  	}
docs: The system_id parameter is used to identify an ESME ( External Short
  Message Entity) or an SMSC (Short Message Service Centre) at bind time.
  An ESME system_id identifies the ESME or ESME agent to the SMSC. The SMSC
  system_id provides an identification of the SMSC to the ESME.
  
  You can specify a direct value. For example:
  
  <pre>
  .systemId("foo");
  </pre>
  
  <p>
  You can also specify one or several property keys. For example:
  
  <pre>
  .systemId("${custom.property.high-priority}", "${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 systemId
  one value, or one or several property keys
  @return this instance for fluent chaining