'EnvironmentAndSystemPropertyClientProviderStrategy' should handle empty DOCKER_HOST

[bsideup]

Testcontainers fails to start if DOCKER_HOST is set to an empty string.

Reproducer:

export DOCKER_HOST=
// run the tests

[roulpriya]

Hi,

I'm willing to work on this issue. I tried to reproduce this issue by setting DOCKER_HOST= but the test cases were passing. I was running the tests on MacBook pro m1 with macOS=12.6 and docker desktop= v4.12.0 with Docker version 20.10.17, build 100c701

[kiview]

Hey @roulpriya, great that you want to look into it.

This issue occurs, if docker.host is set in the ~/.testcontainers.properties file (e.g. to a valid value), but DOCKER_HOST is also set and is empty.

It will show such an error:

EnvironmentAndSystemPropertyClientProviderStrategy: failed with exception NullPointerException (Cannot invoke "String.hashCode()" because "<local5>" is null)As no valid configuration was found, execution cannot continue.

The culprit is like this code right here, since it check only for a key, but not for empty value:

testcontainers-java/core/src/main/java/org/testcontainers/utility/TestcontainersConfiguration.java

Lines 232 to 234 in de1324e

	if (environment.containsKey(envVarName)) {
	return environment.get(envVarName);
	}