bigtable: set true/false filters to null when omitted

packages/bigtable/src/filter.js

@@ -765,6 +765,10 @@ Filter.prototype.time = function(time) {
  * execution of the filters will be the order in which they were specified.
  */
 Filter.prototype.toProto = function() {
+  if (!this.filters_.length) {
+    return null;
+  }
+
   if (this.filters_.length === 1) {
     return this.filters_[0];
   }

packages/bigtable/system-test/bigtable.js

@@ -538,6 +538,25 @@ function generateTableName() {
           });
         });
 
+        it('should run a conditional filter with pass only', function(done) {
+          var filter = {
+            condition: {
+              test: [{
+                row: 'gwashington'
+              }],
+              pass: [{
+                all: true
+              }]
+            }
+          };
+
+          TABLE.getRows({ filter: filter }, function(err, rows) {
+            assert.ifError(err);
+            assert(rows.length > 0);
+            done();
+          });
+        });
+
         it('should only get cells for a specific family', function(done) {
           var entries = [{
             key: 'gwashington',

packages/bigtable/test/filter.js

@@ -495,6 +495,13 @@ describe('Bigtable/Filter', function() {
   });
 
   describe('toProto', function() {
+    it('should return null when no filters are present', function() {
+      var filter = new Filter();
+      var filterProto = filter.toProto();
+
+      assert.strictEqual(filterProto, null);
+    });
+
     it('should return a plain filter if there is only 1', function() {
       filter.filters_ = [{}];