diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 0762461d541d5..6a7065377b28e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -56,6 +56,8 @@ The following tools need to be installed on your system prior to installing the
 - [Yarn >= 1.19.1, < 2](https://yarnpkg.com/lang/en/docs/install)
 - [.NET Core SDK 3.1.x](https://www.microsoft.com/net/download)
 - [Python >= 3.6.5, < 4.0](https://www.python.org/downloads/release/python-365/)
+- [Docker >= 19.03](https://docs.docker.com/get-docker/)
+  - the Docker daemon must also be running
 
 First fork the repository, and then run the following commands to clone the repository locally.
 
@@ -113,8 +115,9 @@ However, if you wish to build the the entire repository, the following command w
 
 ```console
 cd <root of the CDK repo>
-yarn build
+scripts/foreach.sh yarn build
 ```
+Note: The `foreach` command is resumable by default; you must supply `-r` or `--reset` to start a new session.
 
 You are now ready to start contributing to the CDK. See the [Pull Requests](#pull-requests) section on how to make your
 changes and submit it as a pull request.
diff --git a/packages/@aws-cdk/aws-lambda-event-sources/lib/stream.ts b/packages/@aws-cdk/aws-lambda-event-sources/lib/stream.ts
index c9de62653a93e..85b9728fafbc2 100644
--- a/packages/@aws-cdk/aws-lambda-event-sources/lib/stream.ts
+++ b/packages/@aws-cdk/aws-lambda-event-sources/lib/stream.ts
@@ -41,7 +41,7 @@ export interface StreamEventSourceProps {
    * * Minimum value of 60 seconds
    * * Maximum value of 7 days
    *
-   * @default Duration.days(7)
+   * @default - the retention period configured on the stream
    */
   readonly maxRecordAge?: Duration;
 
@@ -51,7 +51,7 @@ export interface StreamEventSourceProps {
    * * Minimum value of 0
    * * Maximum value of 10000
    *
-   * @default 10000
+   * @default - retry until the record expires
    */
   readonly retryAttempts?: number;
 
diff --git a/scripts/check-build-prerequisites.sh b/scripts/check-build-prerequisites.sh
old mode 100644
new mode 100755
index c703d9f3e94e7..4414ff378a48d
--- a/scripts/check-build-prerequisites.sh
+++ b/scripts/check-build-prerequisites.sh
@@ -42,7 +42,7 @@ app_v=$(node --version)
 # Check for version 10.*.* - 29.*.*
 echo -e "Checking node version... \c"
 if [ $(echo $app_v | grep -c -E "v[12][0-9]\.[0-9]+\.[0-9]+") -eq 1 ]
-then    
+then
     # Check for version 13.0 to 13.6
     if [ $(echo $app_v | grep -c -E "v13\.[0-6]\.[0-9]+") -eq 1 ]
     then
@@ -50,7 +50,7 @@ then
     else
         # Check for version < 10.13
         if [ $(echo $app_v | grep -c -E "v10\.([0-9]|1[0-2])\.[0-9]+") -eq 1 ]
-        then   
+        then
             wrong_version
         else
             echo "Ok"
@@ -68,7 +68,7 @@ check_which $app $app_min
 app_v=$(${app} --version)
 echo -e "Checking yarn version... \c"
 if [ $(echo $app_v | grep -c -E "1\.(19|2[0-9])\.[0-9]+") -eq 1 ]
-then   
+then
     echo "Ok"
 else
     wrong_version
@@ -83,9 +83,34 @@ check_which $app $app_min
 echo -e "Checking if docker is running... \c"
 docker_running=$(docker ps)
 if [ $? -eq 0 ]
-then    
+then
     echo "Ok"
 else
     die "Docker is not running"
 fi
 
+# [.NET == 3.1.x]
+app="dotnet"
+app_min="3.1.0"
+check_which $app $app_min
+app_v=$(${app} --version)
+echo -e "Checking dotnet version... \c"
+if [ $(echo $app_v | grep -c -E "3\.1\.[0-9]+") -eq 1 ]
+then
+    echo "Ok"
+else
+    wrong_version
+fi
+
+# [Python >= 3.6.5, < 4.0]
+app="python3"
+app_min="3.6.5"
+check_which $app $app_min
+app_v=$(${app} --version)
+echo -e "Checking python3 version... \c"
+if [ $(echo $app_v | grep -c -E "3\.[6-9]+\.[0-9]+") -eq 1 ]
+then
+    echo "Ok"
+else
+    wrong_version
+fi
diff --git a/scripts/check-yarn-lock.js b/scripts/check-yarn-lock.js
index 285128b3b18a6..d13e4e08cf64f 100755
--- a/scripts/check-yarn-lock.js
+++ b/scripts/check-yarn-lock.js
@@ -45,9 +45,9 @@ async function main() {
   }
 
   projects.forEach((p) => {
-    Object.entries(p.devDependencies ?? {}).forEach(([depName, depVersion]) => errorIfNotInYarnLock(p, depName, depVersion));
-    Object.entries(p.peerDependencies ?? {}).forEach(([depName, depVersion]) => errorIfNotInYarnLock(p, depName, depVersion));
-    Object.entries(p.dependencies ?? {}).forEach(([depName, depVersion]) => errorIfNotInYarnLock(p, depName, depVersion));
+    Object.entries(p.devDependencies || {}).forEach(([depName, depVersion]) => errorIfNotInYarnLock(p, depName, depVersion));
+    Object.entries(p.peerDependencies || {}).forEach(([depName, depVersion]) => errorIfNotInYarnLock(p, depName, depVersion));
+    Object.entries(p.dependencies || {}).forEach(([depName, depVersion]) => errorIfNotInYarnLock(p, depName, depVersion));
   });
 }