Improved verification of DOM string IRI (github issue #2).

src/JsonLD/Core/JsonLdProcessor.cs

@@ -66,8 +66,25 @@ public static JArray Expand(JToken input, JsonLdOptions opts)
 		{
 			// 1)
 			// TODO: look into java futures/promises
-			// 2) TODO: better verification of DOMString IRI
-			if (input.Type == JTokenType.String && ((string)input).Contains(":"))
+
+            // 2) verification of DOMString IRI
+            bool isIriString = input.Type == JTokenType.String;
+            if (isIriString)
+		    {
+		        bool hasColon = false;
+		        foreach (var c in ((string) input))
+		        {
+		            if (c == ':')
+		                hasColon = true;
+		            if (!hasColon && (c == '{' || c == '['))
+		            {
+		                isIriString = false;
+                        break;
+		            }
+		        }
+		    }
+
+			if (isIriString)
 			{
 				try
 				{

src/JsonLD/Core/JsonLdUtils.cs

@@ -199,7 +199,7 @@ internal static void MergeCompactedValue(JObject obj, string
 		public static bool IsAbsoluteIri(string value)
 		{
 			// TODO: this is a bit simplistic!
-			return value.Contains(":");
+			return value != null && value.Contains(":");
 		}
 
 		/// <summary>Returns true if the given value is a subject with properties.</summary>

src/JsonLD/Util/JavaCompat.cs

@@ -67,7 +67,7 @@ public static bool SafeCompare<T>(this JToken token, T val)
         {
             try
             {
-                return token.Value<T>().Equals(val);
+                return token == null ? val == null : token.Value<T>().Equals(val);
             }
             catch
             {