"No such library resource" error in JenkinsFile - jenkins

Question

When I run build I get this error:
ERROR SENDING EMAIL hudson.AbortException: No such library resource build/email.html.groovy could be found.
The file "email.html.groovy" is in the same directory.
An error appears on the line:
def fileContents = libraryResource(fileName)
My Groovy file with 2 functions:
package workflowlibs.manager;
import groovy.text.StreamingTemplateEngine
/**
* This method returns a string with the template filled with groovy variables
*/
def emailTemplate(params) {
def fileName = "build/email.html.groovy"
def fileContents = libraryResource(fileName)
def engine = new StreamingTemplateEngine()
return engine.createTemplate(fileContents).make(params).toString()
}
/**
* This method send an email generated with data from Jenkins
* #param buildStatus String with job result
* #param emailRecipients Array with emails: emailRecipients = []
*/
def notifyEmail(buildStatus, emailRecipients) {
try {
def icon = "✅"
def statusSuccess = true
def hasArtifacts = true
if(buildStatus != "SUCCESSFUL") {
icon = "❌"
statusSuccess = false
hasArtifacts = false
}
def body = emailTemplate([
"jenkinsText" : env.JOB_NAME,
"jenkinsUrl" : env.BUILD_URL,
"statusSuccess" : statusSuccess,
"hasArtifacts" : hasArtifacts,
"downloadUrl" : "www.downloadurl.com"
]);
mail (to: emailRecipients.join(","),
subject: "${icon} [ ${env.JOB_NAME} ] [${env.BUILD_NUMBER}] - ${buildStatus} ",
body: body,
mimeType: 'text/html'
);
} catch (e){
println "ERROR SENDING EMAIL ${e}"
}
}
return this;