GeoServer 发布的图层预览不了

<?xml version="1.0" encoding="UTF-8"?>
<StyledLayerDescriptor version="1.0.0" 
 xsi:schemaLocation="http://www.opengis.net/sld StyledLayerDescriptor.xsd" 
 xmlns="http://www.opengis.net/sld" 
 xmlns:ogc="http://www.opengis.net/ogc" 
 xmlns:xlink="http://www.w3.org/1999/xlink" 
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <!-- a Named Layer is the basic building block of an SLD document -->
  <NamedLayer>
    <Name>default_line</Name>
    <UserStyle>
    <!-- Styles can have names, titles and abstracts -->
      <Title>Default Line</Title>
      <Abstract>A sample style that draws a line</Abstract>
      <!-- FeatureTypeStyles describe how to render different features -->
      <!-- A FeatureTypeStyle for rendering lines -->
      <FeatureTypeStyle>
        <Rule>
          <Name>rule1</Name>
          <Title>Blue Line</Title>
          <Abstract>A solid blue line with a 1 pixel width</Abstract>
          <LineSymbolizer>
            <Stroke>
              <CssParameter name="stroke">#0000FF</CssParameter>
            </Stroke>
          </LineSymbolizer>
        </Rule>
      </FeatureTypeStyle>
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  </NamedLayer>
</StyledLayerDescriptor>