don't work qlineargradient for text in QLabel

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i tried everything. in QtDesigner, gradient for QLabel works perfectly, but when i setting style sheet like this :
"* {color: qlineargradient(spreadad, x1:0 y1:0, x2:1 y2:0, stop:0 rgba(0, 0, 0, 255), stop:1 rgba(255, 255, 255, 255));"

dynamically in my code, i have a white text on my label
what am i do wrong?

here, how i do this:

mpExampleLabel = new QLabel(tr("Cell text example"), this);
mpExampleLabel->setFrameStyle(QFrame::Box);
mpExampleLabel->setAlignment(Qt::AlignHCenter|Qt::AlignVCenter);
mpExampleLabel->setStyleSheet("* {color: qlineargradient(spread:pad, x1:0 y1:0, x2:1 y2:0, stop:0 rgba(0, 0, 0, 255), stop:1 rgba(255, 255, 255, 255));");

mpExampleLabel = new QLabel(tr("Cell text example"), this);
mpExampleLabel->setFrameStyle(QFrame::Box);
mpExampleLabel->setAlignment(Qt::AlignHCenter|Qt::AlignVCenter);
mpExampleLabel->setStyleSheet("* {color: qlineargradient(spread:pad, x1:0 y1:0, x2:1 y2:0, stop:0 rgba(0, 0, 0, 255), stop:1 rgba(255, 255, 255, 255));");

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