code: public void setPreviewValue(String previewValue) {
  		if (!isProcedureParameter && (previewValue != null)) {
  			throw new IllegalArgumentException("Parameter '" + name + "' is not a procedure parameter.");
  		}
  		this.previewValue = previewValue;
  	}
docs: Set preview value for procedure parameter Allows to set null for any type
  
  @param previewValue
  preview value for procedure parameter