mysql - IllegalArgumentException: MetaClass not found

Question

I use a framework called "Cuba.Studio" to create a CRUD application.

When I use this JPQL Query, I get this exception:

Error com.haulmont.cuba.core.global.RemoteException: MetaClass not
found for firstusecase$FIRSTUSECASE_USE_CASE_PROJECT_LINK

this is my code:

try (Transaction tx = persistence.createTransaction()) {
    EntityManager em = persistence.getEntityManager();
    Query query = em.createQuery("select firstusecase$Project.name from 
    firstusecase$UseCase useCase, 
    firstusecase$FIRSTUSECASE_USE_CASE_PROJECT_LINK commonTable, 
    firstusecase$Project project where useCase.id = commonTable.use_case_id 
    and project.id = commonTable.project_id and useCase.id = :useCaseId")
                        .setParameter("useCaseId", useCase.getId());

and here is a part of the code of my Entity Class:

    @JoinTable(name = "FIRSTUSECASE_USE_CASE_PROJECT_LINK",
    joinColumns = @JoinColumn(name = "USE_CASE_ID"),
    inverseJoinColumns = @JoinColumn(name = "PROJECT_ID"))
    @ManyToMany
    protected Collection<Project> project;

Does anybody have an idea? I would be very thankful about your support :)

Thanks

EDIT: Here is the code of the UseCase Class

package com.company.firstusecase.entity;

import javax.persistence.Entity;
import javax.persistence.Table;
import java.util.Collection;
import javax.persistence.FetchType;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import com.haulmont.cuba.core.entity.StandardEntity;
import javax.persistence.Column;
import com.haulmont.chile.core.annotations.NamePattern;
import javax.persistence.Lob;
import com.haulmont.chile.core.annotations.MetaProperty;
import javax.persistence.Transient;

    @NamePattern("%s|jamaref")
    @Table(name = "FIRSTUSECASE_USE_CASE")
    @Entity(name = "firstusecase$UseCase")
    public class UseCase extends StandardEntity {
    private static final long serialVersionUID = 4928397068727365740L;

    @Column(name = "JAMAREF", length = 30)
    protected String jamaref;

    @Column(name = "PROJECT_LIST")
    protected String projectList;

    @Transient
    @MetaProperty
    protected String usecaseDescription;

    @Column(name = "CHANGE_TRACKING_COMMENT")
    protected String changeTrackingComment;

    @Lob
    @Column(name = "CHANGE_TRACKING")
    protected String changeTracking;

    @Column(name = "POWERAMSREF", length = 30)
    protected String poweramsref;

    @Column(name = "LEGACYPWRUC", length = 30)
    protected String legacypwruc;

    @Column(name = "TRACKING_CHANGE_COMMENT")
    protected String trackingChangeComment;

    @Column(name = "INSERT_TIMESTAMP")
    protected String insertTimestamp;

    @Column(name = "USECASE_TYPE")
    protected String usecaseType;

    @Column(name = "CHANGE_TIMESTAMP")
    protected String changeTimestamp;

    @JoinTable(name = "FIRSTUSECASE_USE_CASE_PROJECT_LINK",
        joinColumns = @JoinColumn(name = "USE_CASE_ID"),
        inverseJoinColumns = @JoinColumn(name = "PROJECT_ID"))
    @ManyToMany
    protected Collection<Project> project;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "USECASE_STATUS_ID")
    protected UseCaseStatus usecaseStatus;

public void setProjectList(String projectList) {
    this.projectList = projectList;
}

public String getProjectList() {
    return projectList;
}

public String getUsecaseDescription() {
    return usecaseDescription;
}


public void setChangeTrackingComment(String changeTrackingComment) {
    this.changeTrackingComment = changeTrackingComment;
}

public String getChangeTrackingComment() {
    return changeTrackingComment;
}


public void setChangeTracking(String changeTracking) {
    this.changeTracking = changeTracking;
}


public void setInsertTimestamp(String insertTimestamp) {
    this.insertTimestamp = insertTimestamp;
}


public void setChangeTimestamp(String changeTimestamp) {
    this.changeTimestamp = changeTimestamp;
}


public String getInsertTimestamp() {
    return insertTimestamp;
}

public void setUsecaseType(String usecaseType) {
    this.usecaseType = usecaseType;
}

public String getUsecaseType() {
    return usecaseType;
}

public String getChangeTimestamp() {
    return changeTimestamp;
}


public String getChangeTracking() {
    return changeTracking;
}


public void setTrackingChangeComment(String trackingChangeComment) {
    this.trackingChangeComment = trackingChangeComment;
}

public String getTrackingChangeComment() {
    return trackingChangeComment;
}


    public void setUsecaseStatus(UseCaseStatus usecaseStatus) {
        this.usecaseStatus = usecaseStatus;
    }

    public UseCaseStatus getUsecaseStatus() {
        return usecaseStatus;
    }


    public void setJamaref(String jamaref) {
        this.jamaref = jamaref;
    }

    public String getJamaref() {
        return jamaref;
    }

    public void setPoweramsref(String poweramsref) {
        this.poweramsref = poweramsref;
    }

    public String getPoweramsref() {
        return poweramsref;
    }

    public void setLegacypwruc(String legacypwruc) {
        this.legacypwruc = legacypwruc;
    }

    public String getLegacypwruc() {
        return legacypwruc;
    }


    public void setProject(Collection<Project> project) {
        this.project = project;
    }

    public Collection<Project> getProject() {
        return project;
    }


}

And the code of the Project.class

package com.company.firstusecase.entity;

import javax.persistence.Entity;
import javax.persistence.Table;
import javax.persistence.Column;
import com.haulmont.cuba.core.entity.StandardEntity;
import com.haulmont.chile.core.annotations.NamePattern;

@NamePattern("%s|name")
@Table(name = "FIRSTUSECASE_PROJECT")
@Entity(name = "firstusecase$Project")
public class Project extends StandardEntity {
    private static final long serialVersionUID = -3997556855391197754L;

    @Column(name = "NAME", nullable = false)
    protected String name;

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }


}

Thanks