Can't convert a computed Geometry to GeoJSON. Use evaluate() instead

This is my code, and it generates this error. I’m wondering how to fix it.

Can't convert a computed Geometry to GeoJSON. Use evaluate() instead.
    in createNDVIComposite(), line 30
    in <global>, line 57
    in <global>, line 59

---

var roi = roi.geometry();
//==================================//
// LANDSAT NDVI COMPOSITE CREATION //
//==================================//

// NDVI Functions
/*These 2 functions are used to calculate the NDVI for Landsat 5/7 and Landsat 8, respectively.*/
var getNDVI57 = function(image) {
  var ndvi = image.normalizedDifference(['B4', 'B3']);
  return(ndvi);  
};
var getNDVI8 = function(image){
  var ndvi = image.normalizedDifference(['B5', 'B4']);
  return(ndvi); 
 
};


// Main function
var createNDVIComposite = function(){
  var yearrangeStart = 1999;
  var yearrangeStop = 2018;
  var imgList = [];
  for(var loopYear = yearrangeStart; loopYear <= yearrangeStop; loopYear +=1){
    var start = ee.Date.fromYMD(loopYear, 1, 1);
    var end = ee.Date.fromYMD(loopYear, 12, 31);
  
    //Landsat 8
    var l8 = ee.ImageCollection("LANDSAT/LC08/C01/T1_SR") 
      .filterBounds(roi) 
      .filterDate(start, end) 
      .filterMetadata('CLOUD_COVER', 'less_than', 80) 
      .map(getNDVI8);
    
    //Landsat7
    var l7 = ee.ImageCollection("LANDSAT/LE07/C01/T1_SR") 
      .filterBounds(roi) 
      .filterDate(start, end) 
      .filterMetadata('CLOUD_COVER', 'less_than', 80) 
      .map(getNDVI57);
    
    //Landsat5
    var l5 = ee.ImageCollection("LANDSAT/LT05/C01/T1_SR")
      .filterBounds(roi)
      .filterDate(start, end)
      .filterMetadata('CLOUD_COVER', 'less_than', 80)
      .map(getNDVI57);

    //Merge collections
    var mergedCollection = ee.ImageCollection(l8.merge(l7).merge(l5))
                            .reduce(ee.Reducer.median())
                            .reduce(ee.Reducer.percentile([90]));

    var finalOutput = mergedCollection.clip(roi).rename(loopYear.toString());

    imgList.push(finalOutput);
    //Generate filename for export
    var filename = ("Annual_NDVI_"+roi+"_").concat(loopYear.toString());
  }
 
  // Visualization parameters.
  //var ndviParams = {min: -1, max: 1, palette: ['blue', 'white', 'green']};
  var args = {
    crs:'EPSG:3857',
    dimensions: '300',
    region: roi,
    min: -1, 
    max: 1, 
    //palatte: [ndviParams],
    palette: ['blue', 'white','green',' red'],
    framesPerSecond: 2,
  };

  var yearImgCol = ee.ImageCollection.fromImages(imgList);
  
  var thumb = ui.Thumbnail({
    // Specifying a collection for "image" animates the sequence of images.
    image: yearImgCol,
    params: args,
    style: {
      position: 'bottom-right',
      width: '320px'
    }});
  Map.add(thumb);

}

//print(ui.Thumbnail(Class.select('classificacao'), videoArgs));

//-----------------------------------// 
// MAIN FUNCTION EXECUTION // 
//-----------------------------------// 
var comp = createNDVIComposite();