fixed crash when generating multiple encoded codes

Author: ajungg

build.gradle

@@ -24,7 +24,7 @@ allprojects {
     }
 
     project.ext {
-        sdkVersion='0.9.0-beta16'
+        sdkVersion='0.9.0-beta17'
         versionCode=1
 
         compileSdkVersion=28

core/src/androidTest/java/io/snabble/sdk/EncodedCodesGeneratorTest.java

@@ -61,7 +61,7 @@ public void testSplitAtMaxChars() {
         Assert.assertEquals("+foo;bar;baz-", codes.get(0));
         Assert.assertEquals("+asdf-", codes.get(1));
     }
-
+    
     @Test
     @UiThreadTest
     public void testSplitAtMaxCodes() {

core/src/main/java/io/snabble/sdk/encodedcodes/EncodedCodesGenerator.java

@@ -11,10 +11,11 @@ public class EncodedCodesGenerator {
     private EncodedCodesOptions options;
     private boolean addedCodeWithCheck;
 
-    private ArrayList<String> encodedCodes = new ArrayList<>();
+    private ArrayList<String> encodedCodes;
     private int codeCount;
 
     public EncodedCodesGenerator(EncodedCodesOptions encodedCodesOptions) {
+        encodedCodes = new ArrayList<>();
         stringBuilder = new StringBuilder();
         options = encodedCodesOptions;
     }
@@ -35,7 +36,7 @@ public ArrayList<String> generate() {
 
         finishCode();
         ArrayList<String> ret = encodedCodes;
-        encodedCodes = null;
+        encodedCodes = new ArrayList<>();
         return ret;
     }