GWT HTML export from LibGdx shows : GwtApplication: exception: (TypeError) - html

Question

I have an Android game developed with LibGdx version 1.9.9, which I am trying to export in HTML. I am using GWT (V-2.8.2). The game is running well in Android and doesn't have any issues. While exporting the game by running this command ./gradlew html:dist I am not getting any errors.
But when I am placing the exported library into the localhost and trying to access the game, first the default loader is appearing and then there is a blank screen with this error message:
GwtApplication: exception: (TypeError) : null is not an object (evaluating 'null.zY')
(TypeError) : null is not an object (evaluating 'null.zY')
This is happening in every browser - Safari, Chrome, Firefox.
The stack trace doesn't show any significant place of debug.
Any idea of what is the problem? Thanks.
HTML Gradle:
gwt {
gwtVersion='2.8.0' // Should match the gwt version used for building the gwt backend
maxHeapSize="2G" // Default 256m is not enough for gwt compiler. GWT is HUNGRY
minHeapSize="1G"
src = files(file("src/")) // Needs to be in front of "modules" below.
modules 'com.package.gamename.GdxDefinition'
devModules 'com.package.gamename.GdxDefinitionSuperdev'
project.webAppDirName = 'webapp'
compiler {
strict = true;
disableCastChecking = true;
}
}
import org.wisepersist.gradle.plugins.gwt.GwtSuperDev
def HttpFileServer server = null
def httpFilePort = 8080
task startHttpServer () {
dependsOn draftCompileGwt
String output = project.buildDir.path + "/gwt/draftOut"
doLast {
copy {
from "webapp"
into output
}
copy {
from "war"
into output
}
server = new SimpleHttpFileServerFactory().start(new File(output), httpFilePort)
println "Server started in directory " + server.getContentRoot() + ", http://localhost:" + server.getPort()
}
}
task superDev (type: GwtSuperDev) {
dependsOn startHttpServer
doFirst {
gwt.modules = gwt.devModules
}
}
task dist(dependsOn: [clean, compileGwt]) {
doLast {
file("build/dist").mkdirs()
copy {
from "build/gwt/out"
into "build/dist"
}
copy {
from "webapp"
into "build/dist"
}
copy {
from "war"
into "build/dist"
}
}
}
task addSource {
doLast {
sourceSets.main.compileClasspath += files(project(':core').sourceSets.main.allJava.srcDirs)
}
}
tasks.compileGwt.dependsOn(addSource)
tasks.draftCompileGwt.dependsOn(addSource)
sourceCompatibility = 1.6
sourceSets.main.java.srcDirs = [ "src/" ]
eclipse.project {
name = appName + "-html"
}

Answer 1

Enter the superdev mode and activate source mapping and debugging and step through the source in Chrome, that's the way to find these problems.
Start with superdev parameter
Open the game's web page
Hit the arrow button at the top left corner
Hit the "compile" button
Source Maps are available in Chrome now, you get a "real" stack trace.