[FRigVMOperand](API\Plugins\RigVM\RigVMCore\FRigVMOperand) AddExternalVariable ( [FRigVMExtendedExecuteContext](API\Plugins\RigVM\RigVMCore\FRigVMExtendedExecuteContext) & Context, const [FRigVMExternalVariable](API\Plugins\RigVM\RigVMCore\FRigVMExternalVariable) & InExternalVariable, bool bAllowNullMemory )