bugfix: add new variable to query

src/main/java/eu/hbp/mip/controllers/VariablesApi.java

@@ -155,7 +155,7 @@ public class VariablesApi {
         String histogramGroupings = data.getString("histogram_groupings");
 
         MiningQuery query = new MiningQuery();
-        query.setVariables(query.getVariables().add(new Variable(code)));
+        query.addVariable(new Variable(code));
         List<String> groupings = Arrays.asList(histogramGroupings.split(","));
         query.getGrouping().addAll(groupings.stream().map(Variable::new).collect(Collectors.toList()));
         query.setAlgorithm(new Algorithm("histograms", "Histograms", false));

src/main/java/eu/hbp/mip/model/MiningQuery.java

@@ -27,6 +27,8 @@ public class MiningQuery {
         this.variables = variables;
     }
 
+    public  void addVariable(Variable variable) { this.variables.add(variable); }
+
     public List<Variable> getCovariables() {
         return covariables;
     }