improve signature validation

app/javascript/submission_form/signature_step.vue

@@ -683,13 +683,17 @@ export default {
       }
 
       if (this.isSignatureStarted && this.pad.toData().length > 0 && !isValidSignatureCanvas(this.pad.toData())) {
-        alert(this.t('signature_is_too_small_or_simple_please_redraw'))
+        if (this.field.required === true || this.pad.toData().length > 0) {
+          alert(this.t('signature_is_too_small_or_simple_please_redraw'))
 
-        return Promise.reject(new Error('Image too small or simple'))
+          return Promise.reject(new Error('Image too small or simple'))
+        } else {
+          Promise.resolve({})
+        }
       }
 
-      return new Promise((resolve) => {
-        cropCanvasAndExportToPNG(this.$refs.canvas).then(async (blob) => {
+      return new Promise((resolve, reject) => {
+        cropCanvasAndExportToPNG(this.$refs.canvas, { errorOnTooSmall: true }).then(async (blob) => {
           const file = new File([blob], 'signature.png', { type: 'image/png' })
 
           if (this.dryRun) {
@@ -725,6 +729,14 @@ export default {
               return resolve(attachment)
             })
           }
+        }).catch((error) => {
+          if (this.field.required === true) {
+            alert(this.t('signature_is_too_small_or_simple_please_redraw'))
+
+            return reject(error)
+          } else {
+            return resolve({})
+          }
         })
       })
     }