How to draw a line between two points

[cicidad]

how to draw a line between two points, I set other points as NAN, then the lines cannot show,
for these code:

class DummyInd(bt.Indicator):
    lines = ('dummyline',)
    plotinfo = dict(subplot=False,_skipnan=True, plotforce=True, plotname='1stInd',plotymargin=0.1)
    params = (('period', 1),)
    count =0
    def __init__(self):
        self.lines.dummyline = bt.Max(float('NaN'), float('NaN'))
        super(DummyInd, self).__init__()

    def next(self):
        DummyInd.count +=1
        if DummyInd.count % 30==0:
            self.lines.dummyline[0] = self.data.close[0]+1.5
            print(self.lines.dummyline[0])
        else:
        #    self.lines.dummyline[0] = max(float('NaN'), float('NaN'))
            self.lines.dummyline[0] = 10

I get the picture as following:

I want get line as the green line.
but when I use the following code , set other points as NAN, then will get nothing.

    def next(self):
        DummyInd.count +=1
        if DummyInd.count % 30==0:
            self.lines.dummyline[0] = self.data.close[0]+1.5
            print(self.lines.dummyline[0])
        else:
            self.lines.dummyline[0] = max(float('NaN'), float('NaN'))
            #self.lines.dummyline[0] = 10

how to get the lines between 2 points.

[cicidad]

from the document, We can see

_skipnan (bool, default: False): to skip NaN values when plotting and allowing for example to draw a line between 2 distant points generated by an indicator, which has all intermediate values as NaN (default value for new created data points)

I also set the value, but not take effect.
How to draw a line between 2 distant points ????