What does it mean when the QCustomPlot QCPPlottableLegendItem C++ object has been deleted internally due to a RuntimeError?

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When the QCustomPlot QCPPlottableLegendItem C++ object has been deleted internally due to a RuntimeError, it means that an error occurred during the execution of the program, causing the object to be deleted. The RuntimeError usually indicates an issue in the program's logic or an unexpected condition that the program cannot handle. In this case, the QCustomPlot library internally detected the error and attempted to clean up the affected object, resulting in its deletion. As a developer, you should investigate the cause of the RuntimeError to identify and fix the underlying problem.