!6 url参数为空时，sql生成bug

Merge pull request !6 from zhr0001/master

eladmin-common/src/main/java/me/zhengjie/utils/QueryHelp.java

@@ -40,7 +40,7 @@ public class QueryHelp {
                     String attributeName = isBlank(propName) ? field.getName() : propName;
                     Class<?> fieldType = field.getType();
                     Object val = field.get(query);
-                    if (ObjectUtil.isNull(val)) {
+                    if (ObjectUtil.isNull(val) || "".equals(val)) {
                         continue;
                     }
                     Join join = null;