Error building jar on netbeans

I'm trying to clean and build my project in netbeans but it returns me the following error

/home/foxwalker/NetBeansProjects/Odontologia/nbproject/build-impl.xml:982: Existing manifest /home/foxwalker/NetBeansProjects/Odontologia/build/null875466701 is invalid
FALHA NA CONSTRUÇÃO (tempo total: 2 segundos)

while checking the source of the error:

 <target depends="init,-do-jar-create-manifest,-do-jar-copy-manifest" if="do.archive+main.class.available" name="-do-jar-set-mainclass">
   Erro aqui >>>>     <manifest encoding="UTF-8" file="${tmp.manifest.file}" mode="update">
            <attribute name="Main-Class" value="${main.class}"/>
        </manifest>
    </target>

I'm new and I do not understand well ...