fix(wms): 修复重量输入框精度问题并统一初始化值

将重量输入框的精度设置为3位小数，确保数据一致性
将null初始化值改为undefined，避免潜在的类型问题

klp-ui/src/views/wms/coil/merge.vue

@@ -173,15 +173,14 @@
                   clearable :disabled="readonly || !targetCoil.materialType" />
                 <div v-else>请先选择物料类型</div>
               </el-form-item>
-
               <el-form-item label="毛重(t)">
-                <el-input-number :controls="false" v-model="targetCoil.grossWeight" placeholder="请输入毛重" type="number" step="0.01"
+                <el-input-number precision="3" :controls="false" v-model="targetCoil.grossWeight" placeholder="请输入毛重" type="number" step="0.01"
                   :disabled="readonly">
                   <template slot="append">吨</template>
                 </el-input-number>
               </el-form-item>
               <el-form-item label="净重(t)">
-                <el-input-number :controls="false" v-model="targetCoil.netWeight" placeholder="请输入净重" type="number" step="0.01"
+                <el-input-number precision="3" :controls="false" v-model="targetCoil.netWeight" placeholder="请输入净重" type="number" step="0.01"
                   :disabled="readonly">
                   <template slot="append">吨</template>
                 </el-input-number>
@@ -370,9 +369,9 @@ export default {
           materialName: '',
           productName: '',
           specification: '',
-          grossWeight: null,
-          netWeight: null,
-          length: null,
+          grossWeight: undefined,
+          netWeight: undefined,
+          length: undefined,
           bomItems: []
         },
         {
@@ -386,9 +385,9 @@ export default {
           materialName: '',
           productName: '',
           specification: '',
-          grossWeight: null,
-          netWeight: null,
-          length: null,
+          grossWeight: undefined,
+          netWeight: undefined,
+          length: undefined,
           bomItems: []
         }
       ];