Starting with Michael's comments

app/node-app/arraymap-beacon/v0.3/beacon-query.js

@@ -83,9 +83,14 @@ function buildMongoQuery(params) {
 
     var length = 0;
     if(params.alternateBases == 'DEL') {
-        length = (params.length.length == 0 ? 0 : parseInt(params.length));
+        if (typeof params.length != undefined && params.length != null && params.length != '')
+        {
+            length = (params.length.length == 0 ? 0 : parseInt(params.length));
+        }
     }
 
+    console.log("*** LENGTH: " + length);
+
     var andConditions = [];
     var orConditions  = [];
 

app/node-app/public/js/index.js

@@ -23,7 +23,7 @@ arrayMap.controller('BeaconController', ['$scope', '$location', function ($scope
         "reference": "GRCh38",
         "dataset": "all",
         "alternateBases": "DEL",
-        "length": ''
+        "length": '1'
     }
 
     $scope.getNewApiUrl = function () {

app/node-app/public/partials/beacon-home.html

@@ -49,9 +49,9 @@
             </div>
         </div>
         <div class="form-group">
-            <label for="position" class="col-sm-2 control-label">Length</label>
+            <label for="position" class="col-sm-2 control-label">Minimal Length</label>
             <div class="col-sm-4">
-                <input type="text" class="form-control" id="length" ng-model="config.length" placeholder="Length">
+                <input type="text" class="form-control" id="length" ng-model="config.length">
             </div>
         </div>
         <div class="form-group">