Blob.lastModifiedDate declared as String but browser returns JS Date object — breaks with GWT 2.13

[ihorshu]

Blob.java declares lastModifiedDate as public String in a @jstype(isNative=true) class:

@JsType(isNative = true, name = "Blob", namespace = JsPackage.GLOBAL)
public class Blob {
    @JsProperty
    public String lastModifiedDate;
    // ...
}

However, the browser's File.lastModifiedDate returns a JS Date object, not a string. This type mismatch has always been present but was harmless until GWT 2.13.

What breaks in GWT 2.13:

GWT 2.13 added CharSequence.isEmpty() as a default method (gwtproject/gwt#10091). The devirtualizer now emits a runtime instanceOfString check:

// Generated JS for isEmpty() call in convertUploadFile()
instanceOfString(this$static)
    ? String.$isEmpty(this$static)      // string path
    : this$static.isEmpty__Z();          // non-string path ← crashes here

Since file.lastModifiedDate is a JS Date at runtime, typeof date === 'string' is false, and Date.isEmpty__Z() doesn't exist → TypeError.

The crash occurs in MaterialFileUploader.convertUploadFile():

if (file.lastModifiedDate != null && !file.lastModifiedDate.isEmpty()) {
    lastModifiedDate = new Date(file.lastModifiedDate);
}

Additional note: File.lastModifiedDate is deprecated in the browser API. The modern replacement is File.lastModified which returns a numeric timestamp (milliseconds since epoch).

Suggested fix:

Replace the String lastModifiedDate field in Blob.java with the modern numeric API, and update convertUploadFile():

// In Blob.java — replace:
//   public String lastModifiedDate;
// with:
@JsProperty
public double lastModified;

// In MaterialFileUploader.convertUploadFile() — replace the date parsing with:
Date lastModifiedDate = new Date((long) file.lastModified);

This uses the modern, non-deprecated browser API and avoids calling any Java String methods on native JS values.

Environment: GWT 2.13.0, gwt-material-addins 2.8.5

Ref: gwtproject/gwt#10298