code: @SuppressWarnings("unchecked")
  	@Override
  	public T isNull(final String col) {
  		context().param(CaseFormat.CAMEL_CASE.convert(col), new IsNull(col));
  		this.useOperator = true;
  		return (T) this;
  	}
docs: {@inheritDoc}
  
  @see jp.co.future.uroborosql.fluent.ExtractionCondition#isNull(java.lang.String)