Delaunay triangulation returning empty geometry in PyQGIS

I would like to compute the Delaunay Triangulation for polylines. But sometimes it works and sometimes it does not, I tried with hand drawn lines.

lines=QgsProject.instance().mapLayersByName("lines")[0]
for line in lines.getFeatures():
    print(line.geometry().delaunayTriangulation(0.01, False).asMultiPolygon())

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I tried a cross product collinearity test but I did not have a product equal to 0 and I still have empty geometry

from PyQt5 import *
from math import *
def modulo(a,b):
    if b!=0:
        return a-(int(a/b)*b)
    else:
        return -1
lines=QgsProject.instance().mapLayersByName("lines")[0]

for line in lines.getFeatures():
     n = len(list(line.geometry().vertices()))
     delaunay = line.geometry().delaunayTriangulation(0.01, False)
     i = str(line.id())
     if n <= 2:
         print("Line ID: " + i + " - not enough vertices for Delaunay triangulation")
     elif delaunay.isEmpty():
         print("Line ID: " + i + " - possible collinear vertices")
     else:
         print(delaunay.asGeometryCollection())

m=len(line.geometry().asPolyline())
pts=line.geometry().asPolyline()
for i in range(0,m):
    i1=modulo((i+1),m)
    i2=modulo((i+2),m)
    x1=pts[i1][0]-pts[i][0]
    y1=pts[i1][1]-pts[i][1]
    x2=pts[i2][0]-pts[i1][0]
    y2=pts[i2][1]-pts[i1][1]
    print(x1*y2-y1*x2)#if collinear then vector product=0
    #print(x1*x2+y1*y2)#scalar product

lines=QgsProject.instance().mapLayersByName("lines")[0]

for line in lines.getFeatures():
    n = len(list(line.geometry().vertices()))
    delaunay = line.geometry().delaunayTriangulation(0.01, False)
    i = str(line.id())
    if n <= 2:
        print("Line ID: " + i + " - not enough vertices for Delaunay triangulation")
    elif delaunay.isEmpty():
        print("Line ID: " + i + " - possible collinear vertices")
    else:
        print(delaunay.asGeometryCollection())