title: Testing for an empty parameter in a SAS Macro
body: <p>For example, i have a macro program </p>
  
  <pre><code>%macro test(parameter1= , parameter2=, parameter3=);
    DATA data_gender;
    SET data_input(WHERE=(gender=parameter3));
    RUN;
    .....
  %mend;
  </code></pre>
  
  <p>Basically, i made a selection of observations using the parameter3 (Male or Female). Now i want to create a third option: to keep both observations in Male and Female when the parameter3 is empty (without declaring the value of this parameter). </p>
  
  <pre><code>%test(parameter1=xxx , parameter2=yyy, parameter3=);
  </code></pre>
  
  <p>Can you tell me how can i do that please? </p>