Exception in wasm compiler

[Dogini]

I tried to do the Hello World example and got the folllowing exception:

....
scan java/util/HashMap.get(Ljava/lang/Object;)Ljava/lang/Object;
type: java/util/HashMap
type: java/util/HashMap$Node
call: java/util/HashMap.getNode(Ljava/lang/Object;)Ljava/util/HashMap$Node;
scan java/lang/StringLatin1.charAt([BI)C
call: java/lang/StringIndexOutOfBoundsException.(I)V
scan java/lang/StringUTF16.charAt([BI)C
call: java/lang/StringUTF16.checkIndex(I[B)V
scan java/lang/ref/Reference.refersTo0(Ljava/lang/Object;)Z

WASM compile failed with: Native methods cannot be compiled to WebAssembly: java/lang/ref/Reference.refersTo0(Ljava/lang/Object;)Z
If you want to use classes with native code, you must use a library that implements these native methods, such as 'de.inetsoftware:jwebassembly-api:+' or implements this native method self.
at java.lang.ref.Reference.refersTo0(Reference.java)

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':WASM-Lib:wasm'.

Native methods cannot be compiled to WebAssembly: java/lang/ref/Reference.refersTo0(Ljava/lang/Object;)Z
If you want to use classes with native code, you must use a library that implements these native methods, such as 'de.inetsoftware:jwebassembly-api:+' or implements this native method self.
at java.lang.ref.Reference.refersTo0(Reference.java)

What am I doing wrong?
Here is my build.gradle file:

buildscript {
repositories {
maven { url uri('https://jitpack.io') }
}
dependencies {
classpath 'com.github.i-net-software:jwebassembly-gradle:master-SNAPSHOT'
}
}

apply plugin: "de.inetsoftware.jwebassembly"

repositories {
mavenCentral()
maven {
url = uri('https://jitpack.io')
}
}

dependencies {
implementation 'com.github.i-net-software:jwebassembly-api:master-SNAPSHOT'
}

sourceSets {
main {
java {
srcDir 'src/main/java'
}
}
}

wasm {
//Get more debug information if there are problems.
//logging.level = LogLevel.DEBUG
logging.levelInternal = LogLevel.DEBUG

//Change the output format to the text format *.wat.
//This can be helpful to understand the problems if you see the generated code as text format.
format = 'text'

//The used JWebAssembly compiler version. The default is the latest release '+'.
//You can set any valid Gradle version string or a full dependency string.
//The snapshot version is recommended until a stable release.
//compilerVersion = 0.4
compilerVersion = 'com.github.i-net-software:jwebassembly:master-SNAPSHOT'

//Write method and parameter names into the output *.wasm file.
//The file will be approximate 10% larger. And it generate a source map.
//With a source map you can see in the debugger of the browser your source code if available.
debugNames = true

//Set an absolute or relative path between the final wasm file location and the source files location.
///This is needed for debugging in the browser. It work only if debugNames = true.
//sourceMapBase = '../../src/main/java/'
sourceMapBase = '/src/main/java/'

//set the destination dir
destinationDir = file( 'targetDir' )

//ignore all referenced native methods without declared replacement in a library and replace them with a stub that throws an exception at runtime
//ignoreNative = true
}

[Horcrux7]

WASM compile failed with: Native methods cannot be compiled to WebAssembly: java/lang/ref/Reference.refersTo0(Ljava/lang/Object;)Z

This is a problem with Java 9 or higher if you referenced a String. A pull request for API project that can fix this is welcome.