Merge pull request #193 from Saikedo/master

 'boolean java.lang.String.isEmpty()' on a null object reference on certain Android phones.

Author: RonRadtke

android/src/main/java/com/ReactNativeBlobUtil/ReactNativeBlobUtilReq.java

@@ -297,7 +297,7 @@ public void run() {
 
         // find cached result if `key` property exists
         String cacheKey = this.taskId;
-        String ext = this.options.appendExt.isEmpty() ? "" : "." + this.options.appendExt;
+        String ext = (this.options.appendExt == null || this.options.appendExt.isEmpty()) ? "" : "." + this.options.appendExt;
 
         if (this.options.key != null) {
             cacheKey = ReactNativeBlobUtilUtils.getMD5(this.options.key);
@@ -402,7 +402,7 @@ else if (value.equalsIgnoreCase("utf8"))
 
                 if (rawRequestBodyArray != null) {
                     requestType = RequestType.Form;
-                } else if (cType.isEmpty()) {
+                } else if (cType == null || cType.isEmpty()) {
                     if (!cType.equalsIgnoreCase("")) {
                         builder.header("Content-Type", "application/octet-stream");
                     }

android/src/main/java/com/ReactNativeBlobUtil/Utils/MimeType.java

@@ -27,7 +27,7 @@ public class MimeType {
     public static String getFullFileName(String name, String mimeType) {
         // Prior to API 29, MimeType.BINARY_FILE has no file extension
         String ext = MimeType.getExtensionFromMimeType(mimeType);
-        if (ext.isEmpty() || name.endsWith("." + "ext")) return name;
+        if ((ext == null || ext.isEmpty()) || name.endsWith("." + "ext")) return name;
         else {
             String fn = name + "." + ext;
             if (fn.endsWith(".")) return StringUtils.stripEnd(fn, ".");