Hello evetyone.
Today I have faces the following error:
$ sdkmanager
Warning: Could not create settings

java.lang.IllegalArgumentException at com.android.sdklib.tool.sdkmanager.SdkManagerCliSettings.(SdkManagerCliSettings.java:428) at
com.android.sdklib.tool.sdkmanager.SdkManagerCliSettings.createSettings(SdkManagerCliSettings.java:152) at
com.android.sdklib.tool.sdkmanager.SdkManagerCliSettings.createSettings(SdkManagerCliSettings.java:134) at
com.android.sdklib.tool.sdkmanager.SdkManagerCli.main(SdkManagerCli.java:57) at
com.android.sdklib.tool.sdkmanager.SdkManagerCli.main(SdkManagerCli.java:48)


If you are reading this asticle, it looks like you faced the same. To resolve the issue run following command: {path_to_sdk/tools}/sdkmanager --sdk_root=${ANDROID_HOME} "tools"  

I hope this article will safe your time. Enjoy!