code: public void setDefault(String category, String key, String value) {
  		if (this.hasProperty(category, key)) return;
  		this.setProperty(category, key, value);
  	}
docs: Sets the property, unless it already had a value
  
  @param category The category of the property
  @param key      The identifier of the property
  @param value    The value to set to the property