TypeError: Cannot read property 'substr' of undefined #283

Environment
✔ Getting NativeScript components versions information...
✔ Component nativescript has 7.0.11 version and is up to date.
✔ Component @nativescript/core has 7.0.13 version and is up to date.
✔ Component @nativescript/ios has 7.0.6 version and is up to date.
✔ Component @nativescript/android has 7.0.1 version and is up to date.

Describe the bug
nativescript-ui-chart on NS7 causes this error: TypeError: Cannot read property 'substr' of undefined wich comes from this package (https://github.com/NativeScript/theme/blob/master/src/index.js#L113).
it seems that the property currentMode does not exist anymore in the Theme class