public String getProperty(String key, String defaultValue) {
		return this.properties.getProperty(key, defaultValue);
	}
Return the property for the key, or the default value if the
property doesn't exist.
@param key The key.
@param defaultValue The default value.
@return The property or default value.
spring-xd-messagebus-spi/src/main/java/org/springframework/xd/dirt/integration/bus/AbstractBusPropertiesAccessor.java