diff --git a/.gitignore b/.gitignore
index 524f096..000ce26 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,6 +7,8 @@
 # BlueJ files
 *.ctxt
 
+/target
+
 # Mobile Tools for Java (J2ME)
 .mtj.tmp/
 
@@ -22,3 +24,5 @@
 # virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
 hs_err_pid*
 replay_pid*
+.idea
+DS_store
\ No newline at end of file
diff --git a/src/main/java/io/github/eocqrs/ohip/EnvironmentEnvelope.java b/src/main/java/io/github/eocqrs/ohip/EnvironmentEnvelope.java
index 8ca9602..c8909b2 100644
--- a/src/main/java/io/github/eocqrs/ohip/EnvironmentEnvelope.java
+++ b/src/main/java/io/github/eocqrs/ohip/EnvironmentEnvelope.java
@@ -1,5 +1,6 @@
 package io.github.eocqrs.ohip;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -68,7 +69,7 @@ protected EnvironmentEnvelope(
   }
 
   @Override
-  public final Map<String, String> value() throws Exception {
+  public final Map<String, String> value() {
     final Map<String, String> vars = new HashMap<>(6);
     vars.put("hostname", this.hostname);
     vars.put("app", this.app);
@@ -76,6 +77,6 @@ public final Map<String, String> value() throws Exception {
     vars.put("username", this.username);
     vars.put("password", this.password);
     vars.put("hotel", this.hotel);
-    return vars;
+    return Collections.unmodifiableMap(vars);
   }
 }