fix setting a property to a falsy value with message send

src/Kernel-Tests.js

@@ -6064,6 +6064,42 @@ referencedClasses: ["MessageNotUnderstood"]
 }),
 globals.JSObjectProxyTest);
 
+smalltalk.addMethod(
+smalltalk.method({
+selector: "testSetPropertyWithFalsyValue",
+protocol: 'tests',
+fn: function (){
+var self=this;
+var jsObject;
+return smalltalk.withContext(function($ctx1) { 
+var $1,$2,$3;
+jsObject=self._jsObject();
+$1=_st(jsObject)._a();
+$ctx1.sendIdx["a"]=1;
+self._assert_equals_($1,(1));
+$ctx1.sendIdx["assert:equals:"]=1;
+_st(jsObject)._a_((0));
+$ctx1.sendIdx["a:"]=1;
+$2=_st(jsObject)._a();
+$ctx1.sendIdx["a"]=2;
+self._assert_equals_($2,(0));
+$ctx1.sendIdx["assert:equals:"]=2;
+_st(jsObject)._a_("");
+$ctx1.sendIdx["a:"]=2;
+$3=_st(jsObject)._a();
+$ctx1.sendIdx["a"]=3;
+self._assert_equals_($3,"");
+$ctx1.sendIdx["assert:equals:"]=3;
+_st(jsObject)._a_(false);
+self._assert_equals_(_st(jsObject)._a(),false);
+return self}, function($ctx1) {$ctx1.fill(self,"testSetPropertyWithFalsyValue",{jsObject:jsObject},globals.JSObjectProxyTest)})},
+args: [],
+source: "testSetPropertyWithFalsyValue\x0a\x09| jsObject |\x0a\x09jsObject := self jsObject.\x0a\x09self assert: (jsObject a) equals: 1.\x0a\x0a\x09jsObject a: 0.\x0a\x09self assert: (jsObject a) equals: 0.\x0a\x09jsObject a: ''.\x0a\x09self assert: (jsObject a) equals: ''.\x0a\x09jsObject a: false.\x0a\x09self assert: (jsObject a) equals: false\x0a\x0a\x0a\x09",
+messageSends: ["jsObject", "assert:equals:", "a", "a:"],
+referencedClasses: []
+}),
+globals.JSObjectProxyTest);
+
 smalltalk.addMethod(
 smalltalk.method({
 selector: "testValue",

src/Kernel-Tests.st

@@ -1749,6 +1749,19 @@ testPropertyThatReturnsUndefined
 	self assert: object e isNil
 !
 
+testSetPropertyWithFalsyValue
+	| jsObject |
+	jsObject := self jsObject.
+	self assert: (jsObject a) equals: 1.
+
+	jsObject a: 0.
+	self assert: (jsObject a) equals: 0.
+	jsObject a: ''.
+	self assert: (jsObject a) equals: ''.
+	jsObject a: false.
+	self assert: (jsObject a) equals: false
+!
+
 testValue
 	| testObject |
 	testObject := self jsObject.

support/boot.js

@@ -1042,7 +1042,7 @@ define("amber_vm/boot", [ 'require', './browser-compatibility' ], function (requ
 			if(typeof jsProperty === "function" && !/^[A-Z]/.test(jsSelector)) {
 				return jsProperty.apply(receiver, args);
 			} else if(jsProperty !== undefined) {
-				if(args[0]) {
+				if(args[0] !== undefined) {
 					receiver[jsSelector] = args[0];
 					return nil;
 				} else {