code: public CloudhopperBuilder systemType(String... systemType) {
  		for (String s : systemType) {
  			if (s != null) {
  				systemTypes.add(s);
  			}
  		}
  		return this;
  	}
docs: The system_type parameter is used to categorize the type of ESME that is
  binding to the SMSC. Examples include “VMS” (voice mail system) and “OTA”
  (over-the-air activation system). Specification of the system_type is
  optional - some SMSC’s may not require ESME’s to provide this detail. In
  this case, the ESME can set the system_type to NULL. The system_type
  (optional) may be used to categorize the system, e.g., “EMAIL”, “WWW”,
  etc.
  
  You can specify a direct value. For example:
  
  <pre>
  .systemType("foo");
  </pre>
  
  <p>
  You can also specify one or several property keys. For example:
  
  <pre>
  .systemType("${custom.property.high-priority}", "${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 systemType
  one value, or one or several property keys
  @return this instance for fluent chaining