Removed the skipNullAttributes option.

null attributes are now skipped by default. Added the `keepNullAttributes` option in case someone needs the old behavior.

BREAKING CHANGE: `skipNullAttributes` option removed.

src/XMLAttribute.coffee

@@ -14,8 +14,6 @@ module.exports = class XMLAttribute
 
     if not name?
       throw new Error "Missing attribute name. " + @debugInfo(name)
-    if not value?
-      throw new Error "Missing attribute value. " + @debugInfo(name)
 
     @name = @stringify.attName name
     @value = @stringify.attValue value

src/XMLDocument.coffee

@@ -12,8 +12,8 @@ module.exports = class XMLDocument extends XMLNode
   #
   # `options.skipNullNodes` whether nodes with null values will be ignored:
   #     true or false
-  # `options.skipNullAttributes` whether attributes with null values will be
-  #     ignored: true or false
+  # `options.keepNullAttributes` whether attributes with null values will be
+  #     kept or ignored: true or false
   # `options.ignoreDecorators` whether decorator strings will be ignored when
   #     converting JS objects: true or false
   # `options.separateArrayItems` whether array items are created as separate

src/XMLDocumentCB.coffee

@@ -29,8 +29,8 @@ module.exports = class XMLDocumentCB
   #
   # `options.skipNullNodes` whether nodes with null values will be ignored:
   #     true or false
-  # `options.skipNullAttributes` whether attributes with null values will be
-  #     ignored: true or false
+  # `options.keepNullAttributes` whether attributes with null values will be
+  #     kept or ignored: true or false
   # `options.ignoreDecorators` whether decorator strings will be ignored when
   #     converting JS objects: true or false
   # `options.separateArrayItems` whether array items are created as separate
@@ -91,9 +91,6 @@ module.exports = class XMLDocumentCB
 
     name = getValue name
 
-    if attributes == null and not text?
-      [attributes, text] = [{}, null]
-
     attributes ?= {}
     attributes = getValue attributes
     # swap argument order: text <-> attributes
@@ -138,7 +135,9 @@ module.exports = class XMLDocumentCB
         @attribute attName, attValue
     else
       value = value.apply() if isFunction value
-      if not @options.skipNullAttributes or value?
+      if @options.keepNullAttributes and not value?
+        @currentNode.attributes[name] = new XMLAttribute @, name, ""
+      else if value?
         @currentNode.attributes[name] = new XMLAttribute @, name, value
 
     return @

src/XMLElement.coffee

@@ -66,7 +66,9 @@ module.exports = class XMLElement extends XMLNode
         @attribute attName, attValue
     else
       value = value.apply() if isFunction value
-      if not @options.skipNullAttributes or value?
+      if @options.keepNullAttributes and not value?
+        @attributes[name] = new XMLAttribute @, name, ""
+      else if value?
         @attributes[name] = new XMLAttribute @, name, value
 
     return @

src/index.coffee

@@ -21,8 +21,8 @@ XMLStreamWriter = require './XMLStreamWriter'
 #     true or false
 # `options.skipNullNodes` whether nodes with null values will be ignored:
 #     true or false
-# `options.skipNullAttributes` whether attributes with null values will be
-#     ignored: true or false
+# `options.keepNullAttributes` whether attributes with null values will be
+#     kept or ignored: true or false
 # `options.ignoreDecorators` whether decorator strings will be ignored when
 #     converting JS objects: true or false
 # `options.separateArrayItems` whether array items are created as separate
@@ -59,8 +59,8 @@ module.exports.create = (name, xmldec, doctype, options) ->
 #
 # `options.skipNullNodes` whether nodes with null values will be ignored:
 #     true or false
-# `options.skipNullAttributes` whether attributes with null values will be
-#     ignored: true or false
+# `options.keepNullAttributes` whether attributes with null values will be
+#     kept or ignored: true or false
 # `options.ignoreDecorators` whether decorator strings will be ignored when
 #     converting JS objects: true or false
 # `options.separateArrayItems` whether array items are created as separate

test/basic/attributes.coffee

@@ -36,24 +36,48 @@ suite 'Attributes:', ->
 
   test 'Skip if null attribute (ele)', ->
     eq(
-      xml('test4', { headless: true, skipNullAttributes: true })
-        .ele('node', 'element', {"first":null, 'second': '2'})
+      xml('test4', { headless: true })
+        .ele('node', 'element', {"first": null, "second": '2'})
         .end()
       '<test4><node second="2">element</node></test4>'
     )
 
   test 'Skip if null attribute (att)', ->
     eq(
-      xml('test4', { headless: true, skipNullAttributes: true })
+      xml('test4', { headless: true })
         .ele('node').att("first")
         .end()
       '<test4><node/></test4>'
     )
 
   test 'Skip if null attribute (JSON)', ->
     eq(
-      xml('test4', { headless: true, skipNullAttributes: true })
+      xml('test4', { headless: true })
         .ele({'@first': null, '@second': '2'})
         .end()
       '<test4 second="2"/>'
     )
+
+  test 'Keep null attribute (ele)', ->
+    eq(
+      xml('test4', { headless: true, keepNullAttributes: true })
+        .ele('node', 'element', {"first": null, "second": '2'})
+        .end()
+      '<test4><node first="" second="2">element</node></test4>'
+    )
+
+  test 'Keep null attribute (att)', ->
+    eq(
+      xml('test4', { headless: true, keepNullAttributes: true })
+        .ele('node').att("first")
+        .end()
+      '<test4><node first=""/></test4>'
+    )
+
+  test 'Keep null attribute (JSON)', ->
+    eq(
+      xml('test4', { headless: true, keepNullAttributes: true })
+        .ele({'@first': null, '@second': '2'})
+        .end()
+      '<test4 first="" second="2"/>'
+    )

test/callback/attributes.coffee

@@ -4,22 +4,62 @@ suite 'Attributes:', ->
   data = (chunk, level) ->
     result += chunk
 
-  doc(data)
-    .node('test4')
-      .ele('node', {"first":"1", "second":"2"})
-        .att("third", "3")
+  test 'All forms of att() usage', ->
+    result = ''
+    doc(data)
+      .node('test4')
+        .ele('node', {"first":"1", "second":"2"})
+          .att("third", "3")
+        .up()
+        .ele('node').att({"first":"1", "second":"2"}).up()
       .up()
-      .ele('node').att({"first":"1", "second":"2"}).up()
-    .up()
-    .end()
+      .end()
+
+      eq(
+        result
+
+        '<test4>' +
+          '<node first="1" second="2" third="3"/>' +
+          '<node first="1" second="2"/>' +
+        '</test4>'
+      )
+
+  test 'Skip null attributes', ->
+    result = ''
+    doc(data)
+      .node('test')
+        .ele('node', {"first": null})
+          .att("third", null)
+        .up()
+        .ele('node').att({"first": null}).up()
+      .up()
+      .end()
 
-  test 'All forms of att() usage', ->
     eq(
       result
 
-      '<test4>' +
-        '<node first="1" second="2" third="3"/>' +
-        '<node first="1" second="2"/>' +
-      '</test4>'
+      '<test>' +
+        '<node/>' +
+        '<node/>' +
+      '</test>'
     )
 
+  test 'Keep null attributes', ->
+    result = ''
+    doc({ keepNullAttributes: true }, data)
+      .node('test')
+        .ele('node', {"first": null})
+          .att("second", null)
+        .up()
+        .ele('node').att({"first": null}).up()
+      .up()
+      .end()
+
+    eq(
+      result
+
+      '<test>' +
+        '<node first="" second=""/>' +
+        '<node first=""/>' +
+      '</test>'
+    )

test/guards/attributes.coffee

@@ -1,35 +1,7 @@
 suite 'attribute() Guards:', ->
-  test 'Throw if null attribute (ele)', ->
-    err(
-      () -> xml('test4', { headless: true }).ele('node', 'element', {"first": null, "second":"2"})
-      Error
-      "Missing attribute value. attribute: {first}, parent: <node>"
-    )
-
   test 'Throw if null attribute (att)', ->
     err(
-      () -> xml('test4', { headless: true }).ele('node').att("first")
-      Error
-      "Missing attribute value. attribute: {first}, parent: <node>"
-    )
-
-  test 'Throw if null attribute name (att)', ->
-    err(
-      () -> xml('test4', { headless: true }).ele('node').att(null, "first")
+      () -> xml('test4', { headless: true }).ele('node').att(null, '')
       Error
       "Missing attribute name. parent: <node>"
     )
-
-  test 'Throw if null attribute value (att)', ->
-    err(
-      () -> xml('test4', { headless: true }).ele('node').att("first", null)
-      Error
-      "Missing attribute value. attribute: {first}, parent: <node>"
-    )
-
-  test 'Throw if null attribute (JSON)', ->
-    err(
-      () -> xml('test4', { headless: true }).ele({'@first': null})
-      Error
-      "Missing attribute value. attribute: {first}, parent: <test4>"
-    )