Check for null AppendToResponse

Fix #26

src/main/java/com/omertron/themoviedbapi/methods/TmdbPeople.java

@@ -46,6 +46,7 @@ import com.omertron.themoviedbapi.tools.Param;
 import com.omertron.themoviedbapi.tools.TmdbParameters;
 import java.io.IOException;
 import java.net.URL;
+import org.apache.commons.lang3.StringUtils;
 import org.yamj.api.common.exception.ApiExceptionType;
 
 /**
@@ -80,7 +81,7 @@ public class TmdbPeople extends AbstractMethod {
 
         // Switch combined credits for tv & movie.
         String atr = (String) parameters.get(Param.APPEND);
-        if (atr.contains("combined_credits")) {
+        if (StringUtils.isNotBlank(atr) && atr.contains("combined_credits")) {
             atr = atr.replace("combined_credits", "tv_credits,movie_credits");
             parameters.add(Param.APPEND, atr);
         }
@@ -123,9 +124,11 @@ public class TmdbPeople extends AbstractMethod {
     /**
      * Get the TV credits for a specific person id.
      *
-     * To get the expanded details for each record, call the /credit method with the provided credit_id.
+     * To get the expanded details for each record, call the /credit method with
+     * the provided credit_id.
      *
-     * This will provide details about which episode and/or season the credit is for.
+     * This will provide details about which episode and/or season the credit is
+     * for.
      *
      * @param personId
      * @param language
@@ -152,9 +155,11 @@ public class TmdbPeople extends AbstractMethod {
     /**
      * Get the combined (movie and TV) credits for a specific person id.
      *
-     * To get the expanded details for each TV record, call the /credit method with the provided credit_id.
+     * To get the expanded details for each TV record, call the /credit method
+     * with the provided credit_id.
      *
-     * This will provide details about which episode and/or season the credit is for.
+     * This will provide details about which episode and/or season the credit is
+     * for.
      *
      * @param personId
      * @param language
@@ -228,7 +233,8 @@ public class TmdbPeople extends AbstractMethod {
     /**
      * Get the images that have been tagged with a specific person id.
      *
-     * We return all of the image results with a media object mapped for each image.
+     * We return all of the image results with a media object mapped for each
+     * image.
      *
      * @param personId
      * @param page
@@ -254,7 +260,8 @@ public class TmdbPeople extends AbstractMethod {
      *
      * By default, only the last 24 hours of changes are returned.
      *
-     * The maximum number of days that can be returned in a single request is 14.
+     * The maximum number of days that can be returned in a single request is
+     * 14.
      *
      * The language is present on fields that are translatable.
      *