I have set the "Stretch With Overflow" option True to some text fields , when the data over flow in the jasper viewer is working correctly, the text is on 2 rows but in PDF document the second row is empty: it just adds an empty row.
Exemple xml code :
<textField isStretchWithOverflow="true" isBlankWhenNull="true">
<reportElement positionType="Float" stretchType="RelativeToTallestObject" x="165" y="0" width="35" height="10" isRemoveLineWhenBlank="true" uuid="a5d7ff35-a2dc-480e-80a7-9246d8618b27"/>
<textElement textAlignment="Left">
<font fontName="Futura Std Light" size="7"/>
<paragraph lineSpacing="Single"/>
</textElement>
<textFieldExpression><![CDATA[$F{montant} == null && $F{numeroAppelant} != null ? $F{numeroAppele}.toString():
$F{duree} != null ? $F{duree}.toString() :
$F{volumeKo} != null ? null : $F{montant}.toString()]]>
</textFieldExpression>
I found the solution, I just set the line spacing property to 1.5 !