I'm drawing a curve in P5JS using the beginShape() and endShape() functions. When adding points to my shape (a line) I'm doing so via the curveVertex() function. However, the final curve does not create a segment between points[0] and points[1] for some reason. If I add the points to the curve via the vertex() function instead, the first segment is drawn. Relevant code:

function draw() {
  

  
  // Loop through creating line segments
  beginShape()
  noFill()
  
  // Add the first point
  stroke('black')
  strokeWeight(5)
  curveVertex(x, y)
  
  // Save points, draw last
  let points = []
  points.push({x: x, y: y})
  
  // Draw line
  for (let i = 0; i < segments; i++){
    
    // Get random y
    yRand = random(-(height * 0.125), height * 0.125);
    
    // Add point to curve
    curveVertex(x += length / segments, y += yRand);
    
    // Save point
    points.push({x: x, y: y})
    
  }
  // Draw Last Point
  curveVertex(x, y)
  endShape()
  
  // Draw the last point & segment
  stroke('#ff9900')
  strokeWeight(10)
  points.push({x: x, y: y})
  points.forEach(function(p){
    point(p.x, p.y)
  })
  
  
  // Draw the line once and stop
  noLoop();
}

This produces the following image:

You can see a missing segment between points[0] and points1. Now, if I replace curveVertex() with vertex() in the three places in my code, I get the following image:

As you can see, the first segment is drawn here. If I use endShape(CLOSE) I get the first segment using the curveVertex mode—but also get a line drawn between points[0] and points[-1] (which is unwanted behavior)

My question: what's the difference between vertex() and curveVertex() that would omit the first segment?