diff --git a/README.md b/README.md
index 681792c..bb31b89 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ console.log(template.parameters); // Prints [{ key: "foo" }]
 console.log(template({ foo: "bar" })); // Prints "bar"
 ```
 
-Parameters can have default values, specified using a colon. These come into play when the parameter is either `undefined` or `null`.
+Parameters can have default values, specified using a colon. These come into play only when the parameter is `undefined`.
 
 ```js
 const template = parse("{{foo:bar}}");
diff --git a/index.js b/index.js
index 538156f..c68df12 100644
--- a/index.js
+++ b/index.js
@@ -92,7 +92,8 @@ const parseString = (() => {
         return matches.reduce((result, match, i) => {
           const parameter = parameters[i];
           let value = objectPath.get(context, parameter.key);
-          if (value == null) {
+
+          if (typeof value === 'undefined') {
             value = parameter.defaultValue;
           }
 
@@ -100,7 +101,7 @@ const parseString = (() => {
             value = value();
           }
 
-          if (typeof value === 'object') {
+          if (typeof value === 'object' && value !== null) {
             return value;
           }
 
diff --git a/test.js b/test.js
index 8aaa199..4f4c2c6 100644
--- a/test.js
+++ b/test.js
@@ -326,6 +326,14 @@ describe('json-template', () => {
     });
   });
 
+  describe('date', () => {
+    it('should compute template with Date', () => {
+      const template = parse('{{now}}');
+      const now = new Date();
+      assert.strictEqual(template({ now }), now);
+    });
+  });
+
   // This section tests that arbitrary types may be present
   // as leaf nodes of the object tree, and they are handled correctly.
   describe('unknown types', () => {
@@ -595,26 +603,41 @@ describe('json-template', () => {
     });
   });
 
-  // This section tests that if the match is not found the template should be replaced by null
+  // This section tests that if the match is not found the template should remains undefined
   describe('no match on the given context', () => {
-    it('should replace the given template by null if no match found for an string', () => {
+    it('should replace the given template by undefined if no match found for an string', () => {
       const template = parse('{{foo}}');
-      assert.equal(template({}), null);
+      assert.strictEqual(template({}), undefined);
     });
 
-    it('should replace the given template by null if no match found for an object', () => {
+    it('should replace the given template by undefined if no match found for an object', () => {
       const template = parse({ boo: '{{foo}}' });
-      assert.deepEqual(template({}), { boo: null });
+      assert.deepStrictEqual(template({}), { boo: undefined });
     });
 
     it('should replace the given template by null if the found value is null', () => {
       const template = parse({ boo: '{{foo}}' });
-      assert.deepEqual(template({ foo: null }), { boo: null });
-    });
-
-    it('should handle multi-value expressions where the first value is null, but has a defaultValue', () => {
-      const template = parse({ boo: '{{foo.isNull:defaultValue}} {{foo.isNonNull}}' });
-      assert.deepEqual(template({ foo: { isNull: null, isNonNull: 'value' } }), { boo: 'defaultValue value' });
+      assert.deepStrictEqual(template({ foo: null }), { boo: null });
     });
   });
+
+  describe('string template', () => {
+    it('should be string type when there are more than one slots', () => {
+      const template = parse('{{foo}}{{bar}}');
+      assert.equal(template({ foo: 1, bar: 'a' }), '1a');
+      assert.equal(template({ bar: 'a' }), 'a');
+      assert.equal(template({ foo: 1 }), '1');
+      assert.equal(template({ foo: true, bar: false }), 'truefalse');
+      assert.equal(template({ foo: undefined }), '');
+      assert.equal(template({ foo: null }), '');
+      assert.equal(template({}), '');
+      assert.equal(template(), '');
+      assert.equal(template({ foo: Number.NaN }), 'NaN');
+    });
+
+    it('default value', () => {
+      const template = parse({ boo: '{{foo.isNull:null}} {{foo.isUndefined:undefined}} {{foo.isNonNull}}' });
+      assert.deepStrictEqual(template({ foo: { isNull: null, isNonNull: 'value' } }), { boo: ' undefined value' });
+    });
+  })
 });