Corrected NullPointerException cases occuring in YJsonResponseWriter

when no description is available.

source/net/yacy/server/serverObjects.java

@@ -288,8 +288,13 @@ public class serverObjects implements Serializable, Cloneable {
         put(key, toJSON(value));
     }
 
+    /**
+     * Convert string value to be usable in JSON ouput
+     * @param value value to encode
+     * @return encoded value, empty string when value is null
+     */
     public static String toJSON(String value) {
-        // value = value.replaceAll("\\", "\\\\");
+		if (value != null) {
 			value = patternDoublequote.matcher(value).replaceAll("'");
 			value = patternSlash.matcher(value).replaceAll("\\/");
 			value = patternB.matcher(value).replaceAll("\\b");
@@ -297,6 +302,9 @@ public class serverObjects implements Serializable, Cloneable {
 			value = patternNewline.matcher(value).replaceAll("\\r");
 			value = patternR.matcher(value).replaceAll("\\r");
 			value = patternT.matcher(value).replaceAll("\\t");
+		} else {
+			value = "";
+		}
 		return value;
     }