Add more HL7Parser coverage

rs-e2e/src/main/java/gov/hhs/cdc/trustedintermediary/rse2e/hl7/HL7Parser.java

@@ -53,7 +53,7 @@ public static HL7Message parse(String content) {
     }
 
     public static String parseAndGetValue(List<String> fields, char[] delimiters, int... indices) {
-        if (fields == null || indices[0] > fields.size()) {
+        if (fields == null || fields.isEmpty() || indices[0] > fields.size()) {
             return null;
         }
 

rs-e2e/src/test/groovy/gov/hhs/cdc/trustedintermediary/rse2e/hl7/HL7ParserTest.groovy

@@ -32,4 +32,43 @@ OBX|1|ST|57723-9^Unique bar code number of Current sample^LN||123456||||||F|||20
         message.getValue("NK1", 33, 4, 1, 1) == "Medicaid"
         message.getValue("NK1", 33, 4, 1, 1, 1) == null
     }
+
+    def "parseAndGetValue returns null if a null list of fields is given"() {
+        given:
+        def nullList = null
+        def delimiters = ['|']
+
+        when:
+        def out = HL7Parser.parseAndGetValue(nullList, delimiters as char[])
+
+        then:
+        out == null
+    }
+
+    def "parseAndGetValue returns null if an empty list of fields is given"() {
+        given:
+        def emptyList = []
+        def delimiters = ['|']
+
+        when:
+        def out = HL7Parser.parseAndGetValue(emptyList, delimiters as char[])
+
+        then:
+        out == null
+    }
+
+    def "parseAndGetValue returns null if the indices are pointing outside the expected range"() {
+        given:
+        def emptyList = [
+            "MSH|fakeValues",
+            "OBR|fakeValues"
+        ]
+        def delimiters = ['|']
+
+        when:
+        def out = HL7Parser.parseAndGetValue(emptyList, delimiters as char[], 10, 20)
+
+        then:
+        out == null
+    }
 }