MaterialFileUploader on Errai: Invalid `previewsContainer` option provided. Please provide a CSS selector or a plain HTML element. at Unknown.Dropzone.getElement(

[masterdany88]

When adding file uploader to the page like follow:

	@Inject @DataField private MaterialPanel fileUploaderInput;
	private void initializeFileUploader() {
		MaterialFileUploader fileUploader = new MaterialFileUploader();
		fileUploader.setPreview(false);
        fileUploader.setUrl("/aaaa");
        MaterialUploadLabel uploadLabel = new MaterialUploadLabel("Przeciągnij i upuść aby przesłać pliki", "Some description here");
		fileUploader.add(uploadLabel);
        fileUploaderInput.add(fileUploader);
        fileUploader.reinitialize();
        Window.alert(String.valueOf(fileUploader.isInitialize()));
	}

I am getting an error:

ErraiConsoleLogHandler.java:87 com.google.gwt.core.client.JavaScriptException: (Error) : Invalid `previewsContainer` option provided. Please provide a CSS selector or a plain HTML element.
	at Unknown.Dropzone.getElement(<anonymous>@46761:1)
	at Unknown.new Dropzone(<anonymous>@17374:1)
	at Unknown.Jgm_g$(app-0.js@24:52432)
	at Unknown.Kgm_g$(app-0.js@10:52471)
	at Unknown.EAf_g$(app-0.js@8:50241)
	at Unknown.XWl_g$(app-0.js@21:159156)
	at Unknown.UWl_g$(app-0.js@8:159129)
	at Unknown.onk_g$(app-0.js@17:128243)
	at Unknown.xnk_g$(app-0.js@3:128342)
	at Unknown.xQi_g$(app-0.js@23:99434)
	at Unknown.RPi_g$(app-0.js@19:99138)
	at Unknown.cQi_g$(app-0.js@7:99241)
	at Unknown._Pi_g$(app-0.js@3:99220)
	at Unknown.rnk_g$(app-0.js@3:128284)
	at Unknown.qnk_g$(app-0.js@15:128259)
	at Unknown.aBk_g$(app-0.js@32:133311)
	at Unknown.cBk_g$(app-0.js@17:133353)
	at Unknown.hBk_g$(app-0.js@17:133385)
	at Unknown.cCk_g$(app-0.js@49:133743)
	at Unknown.qFk_g$(app-0.js@59:134599)
	at Unknown.fGk_g$(app-0.js@54:134835)
	at Unknown.kyl_g$(app-0.js@261:151954)
	at Unknown.pul_g$(app-0.js@30:150575)
	at Unknown.qul_g$(app-0.js@8:150588)
	at Unknown.sul_g$(app-0.js@8:150601)
	at Unknown.ful_g$(app-0.js@10:150439)
	at Unknown.Evl_g$(app-0.js@26:151063)
	at Unknown.REd_g$(app-0.js@16:27593)
	at Unknown.SEd_g$(app-0.js@8:27589)
	at Unknown.NDd_g$(app-0.js@8:27266)
	at Unknown._Nd_g$(app-0.js@14:29041)
	at Unknown.FOd_g$(app-0.js@9:29139)
	at Unknown.LOd_g$(app-0.js@8:29212)
	at Unknown.rOd_g$(app-0.js@24:28990)
	at Unknown.ADe_g$(app-0.js@30:41220)
	at Unknown.YDd_g$(app-0.js@28:27337)
	at Unknown.IDe_g$(app-0.js@3:41277)
	at Unknown.Xue_g$(app-0.js@17:38679)
	at Unknown.Wue_g$(app-0.js@3:38668)
	at Unknown.mBe_g$(app-0.js@3:40443)
	at Unknown.jdc_g$(app-0.js@28:19147)
	at Unknown.mdc_g$(app-0.js@16:19203)
	at Unknown.<anonymous>(app-0.js@14:19183)

This was tested only on Errai on versions:

                <errai.version>4.0.0.CR1</errai.version>
		<gwt.version>2.8.0</gwt.version>
		<gwt-material.version>2.0-rc5</gwt-material.version>
		<gwt-material-table.version>1.0-rc3</gwt-material-table.version>

[masterdany88]

Line of code: Window.alert(String.valueOf(fileUploader.isInitialize())); returns false;